If this trade went through, I'd say the Bobcats are still missing a legit big man, particularly a true starting center. Even with Devin Harris they'll still lack shooting and, in general, players who are gifted scorers. No post threat, either.
I don't see them being much better than last year. 1st round exit. Still, trading Diaw and getting back Devin Harris, even if you have to give up some picks, sounds like a solid deal.
The Nets would be a lot better, but they'd be missing a point guard. You need somebody to orchestrate the offense in order to get the ball to the shooters, Melo, and Lopez. Jordan Farmar isn't that guy. I'd expect a dicey first year from that group.
The Nuggets would be significantly worse. Billups becomes the best scorer on the team, which is bad. Unless Favors turns into a real star, they're headed downhill real quick. But they'll be in a much better position than Toronto or Cleveland, so I can't say I'd blame them.
Trade makes sense for Utah, too. AK is injured a lot and makes way more money than he's worth at this point. Not sure how Diaw fits on their roster, though, unless he can really fit in at the 3 (though he'd probably fit as well as AK did, which is to say not great).