ED: Furcal --> Dodgers
Conservatively, Furcal figures to be between a 0 < x > 5 runs defender. Add in, at worst, league average offense and in 600 plate appearances you have between a 2.5-2.7 WAR player. The return should match the investment if the Braves are paying Furcal around 36-40 million through the three guaranteed years, even if Furcal's talents erode as he nears 35. I imagine the vesting option is a typical plate appearances one, which suggests that if Furcal earns it he's been A) healthy enough to play and B) performing well enough to play. If that's the case, there should be no problem with it.
Of course, there's still an inherent injury risk with Furcal. Lower back surgery kept him out most of 2008, but prior to that, Furcal's only other DL stint with the Dodgers came in 2007, when a sprained ankle sidelined him for two weeks. Back surgery is of some concern, especially when Furcal's job description involves scooping up groundballs, but at this point I'd have to defer to medical experts on whether suffering another injury is more likely with his back than say a knee injury. The Braves, A's, Dodgers, and Jays team of medical experts apparently feel (or felt) he was worth the risk, so take that for what it's worth.
Overall, and assuming
Atlanta doesn't do something insane - like pay Furcal 50 million over three years - this is a nice addition.