What do you mean he can't D it up? He's not much of a weakside shotblocker, but he's one of the better post defenders in the league because he's both strong and quick, which makes him extremely versatile on post D. In his career he averages about 2 blocks per 40 minutes, which is better than anyone we have right now.
And yeah, he's been injury plagued, but as has previously been noted, they've been of the freakish variety -- a torn ACL from a bad fall, a bruised leg, a messed up hand, cancer... it's not like he's had microfracture surgery.
I agree the weight gain is somewhat troublesome, but it happens with some players.
Sometimes you have to take risks in trades, and a risk on an athletic 25 year old power forward is one I can get behind.