Where are they now?

    Fortune takes a look back at our '40 under 40' of a decade ago to find out who's still flying high, and who's fallen from grace.

    By Maha Atal and Kim Thai

    Michael Dell

    Age: 43

    Last list appearance: 2004

    Then: Founder and CEO, Dell

    Now: Founder and CEO, Dell

    Talk about a reigning champ: Fortune's original "40 under 40" list was a ranking of net worth, and Dell took the top spot each of the six years we ran the list. Dell, whose eponymous PC firm became the no. 1 PC company in the U.S. in 1999, was worth an estimated $21.49 billion then.

    Today? His net worth is just half that -- with the PC maker having lost share to rivals like Hewlett-Packard and innovative Apple. (Dell has always been notoriously slow on the product development front.) But that's not to say Dell and his company have lost all their glory: The firm still has 14% of the worldwide PC market, trailing only HP. And with the recent announcement that Dell will be entering the smartphone market, the company could be getting the restart it needs.

    Will Smith

    Age: 41

    Last list appearance: 2004

    Then: Actor/producer

    Now: Actor/producer

    The former star of TV's "The Fresh Prince of Bel-Air" made our list in 2004, with a net worth of $188 million. Then 35, he'd become one of Hollywood's biggest box office draws, thanks to hits like Independence Day, Men in Black, and Bad Boys.

    He's now producing big blockbusters like Hitch and Hancock through Overbrook Entertainment, the production company he started in 1997.

    While Smith has been saving the world from robots and vampires on the big screen, some would also argue that he's been helping to save the movie business itself: With more than $2.5 billion in box office sales to his name and Academy Award nominations for his roles in Ali and The Pursuit of Happyness, Smith was also the first actor in Hollywood history to have eight consecutive movies top the $100 million mark.

    Jerry Yang

    Age: 40

    Last list appearance: 2004

    Then: Co-founder and CEO, Yahoo

    Now: Co-founder and Director, Yahoo

    When we last compiled the "40 under 40," Jerry Yang sat on top of the world. Shares of Yahoo had just made a remarkable 200% recovery from their collapse during the economic downturn in 2003, and Yang was gleefully buying up smaller search rivals and fine-tuning Yahoo's e-mail service.

    But Yahoo's two-pronged business - search and mail - was wholly unprepared to compete with the one-stop digital shop offered by Google. Since Google's rise, Yahoo's market share in search, which once seemed insurmountable, has fallen to less than 20%.

    Yang, once the poster child for the dot-com boom, became one of its high-profile casualties: After fighting an unsolicited $44.6 billion takeover bid by Microsoft in February 2008, Yang nearly closed a search deal with Google in the summer. But after the deal fell through, in the wake of a possible antitrust investigation by the Department of Justice -- Yang was asked to step down as Yahoo's CEO. Still he remains a Yahoo director and "Chief Yahoo!"

    Naveen Jain

    Age: 50

    Last list appearance: 1999

    Then: Chairman and CEO, InfoSpace.com

    Now: Co-founder, president, and CEO, Intelius

    Ten years ago, Jain left a lucrative post at Microsoft to "make a billion dollars for myself," as he told Fortune when he appeared on the "40 under 40" list in 1999. That year, Jain -- who cites Bill Gates as his role model --was worth $861 million, and his startup search firm InfoSpace was in its beginning stages.

    Since then, though, Jain has had legal troubles: In 2000, the U.S. Securities and Exchange Commission said that InfoSpace had lost $200 million more than it reported, opening up a bevy of investigations against the company -- and in 2003 Jain was found guilty of insider trading.

    Jain moved on to found Intelius, a website specializing in selling background information about people. But his business practices are being criticized once again: Intelius customers are suing Jain for fraud, claiming Intelius and one of its partners, Adaptive Marketing, stole consumer data to auto-enroll them in various membership programs. Another suit accuses Jain of inflating financial figures. In 2006, the Feds began looking into whether Intelius was illegally disseminating credit card information. A spokesperson for Intelius said the company is "vigorously defending" the class-action litigation and would not comment on the federal investigation.

    Joe Liemandt

    Age: 32

    Last list appearance: 2004

    Then: Founder, president, and CEO, Trilogy

    Now: Founder and CEO, Trilogy

    Like many of the original "40 under 40," Liemandt -- who appeared on all six of our previous lists -- made his riches in the 1990s technology boom. But unlike many of his dot-com peers, Liemandt's venture -- the software service firm Trilogy -- has had staying power.

    That's partly because of his willingness to reinvent. In 2000, when other tech companies famously faltered, Liemandt introduced a new pricing system that allowed clients to pay Trilogy only when its consulting work had an impact on their bottom line. The implicit guarantee kept clients around, and allowed Trilogy to emerge stable when the dot-com bust gave way to a new boom.

    Jeffrey Citron

    Age: 39

    Last list appearance: 2004

    Then: Co-founder, chairman, and CEO, Vonage

    Now: Co-founder and chairman, Vonage

    When we last profiled Citron in 2004 for "40 under 40," he'd already appeared on the list four times, thanks to the wealth he'd amassed from his online brokerage firm Datek. Back then, having settled a $22.5 million trading suit with the SEC, he was gambling on new online phone service Vonage to help rebuild his reputation.

    When the company got off the ground and readied for a public offering in 2006, board members replaced Citron with former Tyco exec Michael Snyder. The move backfired. In Snyder's first year, Vonage saw its share price plummet and lost two patent infringement lawsuits against Verizon and Sprint. To turn the firm around, in April 2007 board members brought in... Citron.

    He may yet succeed: In the second quarter, Vonage eked out a slim $1 million profit - its first quarter in the black since its founding.

    Ted Waitt

    Age: 46

    Last list appearance: 2002

    Then: Co-founder, chairman, and CEO, Gateway

    Now: Founder, Waitt Family Foundation

    The founder and former CEO of Gateway has seen his company grow into a powerhouse. In 2000 -- when at age 37, he was worth an estimated $8.54 billion -- Waitt climbed to No. 2 on our list (after Michael Dell).

    Gateway, like most other technology companies, struggled to stay afloat after the dot-com bust, cutting back production in hopes of turning a profit again. Eventually, in 2004, Gateway acquired low-cost PC-maker eMachines in an effort to save the company, and Waitt handed over day-to-day duties to eMachines CEO Wayne Inouye. Waitt left Gateway the following year and went on to found Avalon Capital Group, an investment company that specializes in technology, healthcare, media and entertainment.

    Arguably though, Waitt is now best-known for his philanthropic work. The Waitt Family Foundation, his own nonprofit, has donated more than $100 million to community building, violence prevention, and other causes.

    Rob Glaser

    Age: 47

    Last list appearance: 2001

    Then: Co-founder, chairman, and CEO, RealNetworks

    Now: Co-founder and CEO, RealNetworks

    As head of RealNetworks, maker of the popular RealPlayer software and Rhapsody music streaming service, Glaser is one of only a few "40 Under 40" alums who still has his old job.

    While his business is still growing, though, the past year has been rough. Last fall, Glaser launched a new service, RealDVD, that lets users copy and store DVD files on their computers. But this summer, a federal judge issued an injunction to ban sales of the software on copyright infringement grounds. (RealNetworks has appealed the decision.)

    Meanwhile, his investment in AirAmerica hasn't worked out as planned. A lifelong liberal, Glaser was among the first and most generous investors in the progressive radio network, but it hasn't become the liberal counterweight to conservative talk radio its founders intended.

    Pierre Omidyar

    Age: 42

    Last list appearance: 2004

    Then: Founder and chairman, eBay

    Now: Founding partner, Omidyar Network

    Pierre Omidyar has the rare distinction of having launched a tech startup -- eBay -- that became exactly the game-changer that its founder intended. After a quick three years as CEO, in 1998 Omidyar turned over the reins to company woman Meg Whitman. Later that year, she handled the company's public offering, which made Omidyar an instant billionaire.

    These days, he's busy with his new career as a philanthropist: Since its inception in 2004, his Omidyar Network has committed $307 million to charities and for-profit startups focused on social change.