Well, I agree with wdleehi on Smith. In my view, Smith is an atrocious man-to-man defender, especially in the post. He's a good cheater/weak side helper and very agressive, but that kind of happy-go-lucky defense doesn't win you many games, although works wonders for fantasy leagues. Smith is like a more reckless and less polished Camby on defense. In fact, he's been so consistently undisciplined on defense during his career that I've started believing he's not the most coachable player in the league, so I don't know if he ever reaches that Camby/Wallace level.
On the offensive end, he's good when attacking the basket or running ISO plays with plenty of room to operate, but his dribble and ballhandling are so poor that he'll only be truly effective in a running team with some good creators and decent spacing. Very subpar player doing everything else. If I was a coach running primarly a half-court motion offense, I have no idea how could I use him. I'd probably change my offensive system.
OTH, he's an exciting player to watch and he's still very young, plenty of room to improve. But right now, from this Atlanta team I'd gladly bring JJ back; I think Horford is going to be really good; but I'm not sure if I'd give anything of value to get Smith.