I'll do it occasionally but I buy less and less from EB Games these days so the temptation isn't very high. Usually you can find the game cheaper when it goes on sale online. Before I had a credit card, though, the most affordable way to get a game was used so I went for it a lot more often.
Now the only reason to buy used is if the game is unavailable new, I suppose. So older games, generally. I'll buy used before I buy digitally at this point, though. I'm thankfully not seriously into it with gaming, but I am a collector at heart and I like seeing all my games on a real shelf. So if I have the option to get a disc and a box, I'll take it before I give up and download the game. (The only exception to no-disc is with PC games where I don't care in the slightest... but you can't really buy those used online anyway so it's a moot point in this thread.)