As a Celtics fan I'm a IT hater, I think a lot of it has to do with visiting this site and seeing everyone complain about him. I hate the hero ball and he's too short to do anything on defense. You guys know him best.
I have mixed emotions about IT. For me, he made a strange transition from the "little overachieving 6th man who could do anything," who I loved, to the guy who wouldn't pass the ball to Cousins or Gay at the end of the game, because he wanted to win the game himself. Things started to go downhill at that point.
I think things would have been fine if they never made him a starter here*. I could be wrong about that, I don't know. But it seemed like as soon as he was able to tell himself "I'm the starting point guard," he was never willingly going back.
The ironic thing is that appears that because of that attitude, he's now been traded away by two teams in less than a year, and he's still not going to start. So he kind of let his ego screw up his plans, in my opinion. And unless he changes his playing style (more facilitating) or decides that "6th Man" is an acceptable role for him, I think he might continue to bounce around the league. To me, he was the next Bobby Jackson, the Kings 6th man during the glory years, and that would have been awesome.
* EDIT: I'm not sure we had much choice at the time, though.