上周四，在LinkedIn上市之日涌现的疯狂买势，令这家职业社交网站的大部分长期投资者发了一笔意外之财，尤其是网站创始人雷德•霍夫曼和其私募股权投资人。

    上周四午盘LinkedIn股价飙升115%，令霍夫曼所持股份价值从8.52亿美元飙升至令人目眩的18亿美元。

    但一位LinkedIn的重要投资者——高盛(Goldman Sachs)，决定远离二级市场的狂欢。事实上这在大股东中也是绝无仅有，高盛决定在上周四LinkedIn上市当天，将所持的全部871,840股股份以IPO价格45美元/股抛出。发生了什么？

    高盛拒绝置评，看上去售罄也未带来巨大经济损失。高盛以IPO价格卖出三年前购入的LinkedIn 股票，总额3,400万美元，肯定是赚钱的。2008年年中，LinkedIn曾以每股5.56美元的价格从首席技术官手中回购股票，因此高盛此次售股的每股盈利可能为39美元左右。

    但上周四LinkedIn的股价大涨说明高盛本应赚得更多。别忘了，在此类价值最大化行动中高盛往往都有出众表现。而且，即便LinkedIn的估值存在泡沫，上周该股的火爆走势似乎也说明泡沫短期内无破灭之虞。

    又或者是高盛认为LinkedIn可能会重蹈本月另一宗热门IPO的覆辙，即5月4日中国社交网站人人网的首日上市之路。IPO价格为14美元/股的人人网首日开盘涨幅超过70%(见上图)，早间更是一度突破24美元。

    但市场热度很快下降。人人网首日收于18美元，较日内高点低25%，并且接下来连跌6个交易日，最低至12.60美元，比IPO价格还低10%。在上周四的社交网站狂欢中，人人网涨4%，但也只是略高于14美元。

    LinkedIn资本狂欢持续的时间很可能长于人人网。但抛售的理由也显而易见，以LinkedIn最近108.55美元/股的股价计，市盈率已高达666倍。

    The LinkedIn (LNKD) buying frenzy Thursday is a windfall for most of the business networking company's longtime shareholders, led by founder Reid Hoffman and his private equity backers.

    The 115% surge in LinkedIn shares at midday Thursday sent the value of Hoffman's stake, for instance, soaring from a merely huge $852 million to a surreal $1.8 billion.

    But one sizable LinkedIn investor, Goldman Sachs (GS), decided to sit out the secondary-market fun. Practically alone among big holders of the stock, Goldman decided to dump it all in Thursday's debut, selling its entire 871,840-share stake at the IPO price of $45 a share. What gives?

    Goldman declined to comment, and it's not like the firm is taking a bath by selling out. Goldman stands to make something on the order of $34 million by selling the LinkedIn shares at the IPO price, three years after it bought the shares. In mid-2008 LinkedIn was paying $5.56 a share to buy back stock from its chief technology officer, so it stands to reason Goldman's per-share profit on this deal is around $39.

    Yet Thursday's blastoff says Goldman could have made even more. The firm's supposed to excel at this sort of value-maximizing activity, after all. And even if LinkedIn's valuation is on the bubbly side, the massive for the stock this week seems to suggest that particular bubble is in no danger of imminent collapse.

    Or is it? Goldman may be banking on a replay of this month's other hot IPO, the May 4 debut of Chinese social networking company Renren (RENN). Its shares jumped more than 70% (see chart, right) when trading started, topping out at $24 early on their first day after pricing at $14.

    But how quickly the Renren craze faded. The stock dropped 25% from its peak on opening day to close at $18, then dropped in each of the next six trading sessions before bottoming out at $12.60, 10% below the IPO price. The stock was up 4% in Thursday's social networking party but is only just above $14.

    LinkedIn mania may well last longer than Renren's run did. But it's easy enough to see the case for selling any stock that is trading, as LinkedIn is at a recent $108.55, at 666 times earnings.