I'd say the fact that Marbury actually wears his shoes in NBA games has convinced me to try a pair. At $15, I've got very little to lose.
I havent' done it, but I had the same thought. If he's actually wearing them in games, they can't be too horrible. And if I hate them, it's only $15.
I like Tmac as a player, and I've bought Tmacs a few times, but I don't think it's because of him. I just buy whatever shoe is the best combination of comfort, looks, and price, in that order.