Nope, I have fairly good control.
I'm super frugal with my money, but the Steam sales are always mighty tempting. I'm surprised I didn't end up getting GTAIV when it was $3 on Steam or whatever over Christmas.
Now that is self control!
Yeah, I grab more things than I would have normally bought. Some sales just go crazy and you can afford to take a risk on some games I wouldn't have otherwise considered. My collection of games on there is a testament to that.
Which I guess is good for consumer and publisher alike. And Steam. It's definitely good for them too.
I can say with complete honesty that I have never once fallen for any steam sale, on account of how much I can't stand 3rd party applications and have plenty of other games to play instead that even if they gave the games out for free it wouldn't be worth the bandwidth cost for how much time I'd have left over to play them. :/