I'll give him a couple of weeks. I know he kept himself in shape over his extended break, but that doesn't mean he isn't rusty. He also may be trying too hard to prove that the Celtics made the right call bringing him in, and that kind of pressing might be affecting his game for the worse.
I don't know, I was one of his biggest detractors back in his New York days. Now Imma just wait and see, but I did notice that in his first games he was holding the ball longer than usual. But like JE says, he has a lot of pressure on him, and now that Rondo's out and he's starting, expectations are all riding on him.
Give Marbury a little more time. He only just started playing, he's gotta get warmed up. I think the Celtics would have won the Heat game had they had either Rondo or KG.
Like I said in another thread, his last game was, I'm pretty sure, December of 2007. Couple that with the him playing with a new team 60 games into the season. His struggles were inevitable. I think he steps it up in postseason.