This Gamasutra article outlines the effect of Steam sales. You'd think that giving big discounts on games would cause losses to the developers, but the thing is that developers are actually making quite a big chunk of money on them.

"We find that we get several thousand percent increases in units and revenue on the days of the Steam sales, and unit sales are usually about double the normal for a few weeks after the sales are over," Runic Games CEO Max Schaefer says."

So how about you - do you Steam at all?