He is going to the heat because that is his best option and he'd be looney not to do so.
Not in my opinion. If his beef truly is about wanting a starting job, or at least lots of minutes, he'd be better off going to Chicago, because he's better than Rip, or the Clippers, because he's better than Randy Foye.
He's not starting in Miami unless Wade goes down with an injury, and I can't see him even getting a lot of minutes, even if the Heat stick with a small lineup—which I imagine would feature Bosh, LeBron, Battier, Wade, Chalmers (a lineup of Bosh, LeBron, Wade, Ray, Chalmers would be too small).
If he stays in Boston, he stills gets 30+ minutes a game, even if he's coming off the bench.