When John Roos left Wilson Sonsini Goodrich & Rosati in May to become U.S. ambassador to Japan, he was forced to leave behind his stake in the law firm’s famed investment fund, WS Investment Co.

In the dot-com heyday, when the fund returned more than the annual salaries of some partners, this might have been a painful exercise. But in recent years, with the slowing economy, the hauls have been less spectacular.