Yes, I also make from time to time my thoughts about that. Especially Federer's forehand out of halffield is such a big weapon, a real canon, the best on the tour; he is also able to put so much spin on, that's really awesome. Just look at what Federer can do with a low slice that drops on the service line or even before into the field. IMO, in such situations, you can't compare Federer's acceleration with his forehand to any other player, that's just huge. And of course he has to do that all mainly with his wrist, but I'm not sure if that automatically means risking a career-ending injury.
Some players are more susceptible to injuries, some are not... so let's hope Roger belongs to the latter category.
BTW, Federer is not the only player... sometimes, I'm also worried about Roddick's arm. How long can he hit thousands of balls every day (okay, I admit it: this is a bit exaggerated *g*) consistently between 120mph and 145mph. When is the back affected, how long can his shoulder, his forearm withstand this constant pressure?
It's no secret that tennis is, for upper body, a very one-sided sport (even more for one-handers).
But let's just hope all these guys don't spend half of their career being injured so that we can enjoy them as long as possible.