If you're someone that Google has decided is an "up", I highly doubt Google is going to let these people go so easily. These people are already being aggressively retained with bonuses and the like.
If you're an "out", well, by definition Yahoo won't be that interested.
And the "ups" that "became outs", so to speak, are people who are of such strong personal conviction that they turned down gobs of money in 2007 from Google to, say, take a riskier position at Facebook or do their own thing. In those cases, it's unlike more gobs of money from Yahoo in 2012 will convince them to jump ship, unless Marissa can offer things to recruits that she couldn't offer to recruits at Google. (This seems unlikely - there was little Google couldn't offer the APMs it lost.)