The exodus at Yahoo continues. Cameron Marlow, a leading light of Yahoo Research, has left its Berkeley building, as we noted — but we can now reveal his destination: Facebook. That Yahoo tried to acquire the social network last year for a fraction of its current $15 billion price just makes his departure more bitter. Marlow, you see, had developed one of the most intriguing social networks at Yahoo — Tagsona, an internal tool for finding coworkers at Yahoo working on similar projects. Tagsona has already inspired social features in Yahoo products — but, alas, its inventor will be cooking up new ideas at Facebook, not Yahoo.