No, I'm with Keric here. Thomas' defense has been awful, and IIRC the on court/off court numbers back that up.
IMO TT's only decent effort on defense came against Minnesota. My guess is that he was pumped up for the challenge of facing Garnett, but more than that, the fact that TT didn't have a lot of help responsibility in that game made him look better than he usually does.
The real answer for Thomas' defensive woes is for him to lose at least 20 pounds, on the "Kurt Thomas diet". Right now TT has the thick upper body of Chris Webber and moves like him, too.
I think D'Antoni has made the right moves with TT so far--first, he showed TT the carrot by putting him into the starting lineup, and now he's showing him the stick by replacing him with JR. The best solution would be to play TT exclusively at center, but his awareness and help defense is so poor...at least TT showed in the Seattle game that he's willing to commit fouls.