Constantly. And for an example of their awesome customer service:
A bunch of us went out to a hockey game (go Sharks!) for my BIL's bday. So my sister orders all ten tickets online at Stubhub. Two days before the game, she gets an email from Stubhub saying that the seller had not shipped the tickets yet, and they would find us comparable or better tickets, or return our money. Day of the game, they called to say they had tickets, or we could download our original seats online. Well, it turns out the new tickets were way better than our old ones, so we went that route. Our original tickets were 42 a piece. The ones Stubhub gave us were 119 a piece, but no cost difference to us. (unfortunately for the seller, if they don't ship the tickets, they are responsible for the cost difference, so our seller would have had to fork out 700 bucks for not sending them out)
I've bought tickets through them a couple times this month alone, and absolutely love them.
Fighting back from the regain
Strong is the new skinny.