Aningan: This was a problem for me but it's slowing getting under control. I just had to realize that it doesn't (shouldn't) mean anything if a game is on an awesome promo. The real currency is time. And that is more limited than my money.
I got 3 games for 1 euro each at the Ubisoft promo earlier this year. Not only I did not play them, I didn't even install them, and not only that but I didn't even open the Uplay client since that promo. Yeah I payed close to nothing for them, but the reality is I will probably never play those games. I don't have time for them. Paying close to nothing is irrelevant when you don't have the "time currency". It doesn't help that those are not in my favorite genres.
So far I've been able to say NO to some great promos, like that Prototype pack which I've caught when it was $7.49 even, and quite a few others.
Starting next year I have a plan that should drastically limit stupid impulse buying. It revolves more around time and less around money.
Main question you have to ask yourself is "Will I play this game by the time the next big promo hits?". If the answer is NO then there is no good reason to buy it.
I have nothing to add to this really, just want to say yes, +1 and this is especially important for people on a tight budget.