I can't be bothered checking exact numbers but I have about 50 games on Steam, most of which came from the Quakecon/Bethesda sale a few months back. Guess how many of those games I've bothered to actually install and play. I reckon 5.
Edit: I did go and check.
41 games.
26 installed.
Of the ones I bothered to install, I have actually played 7 of them - that's including Wolfenstein 3D, which my wife only booted up because she made a copy of the first level in Minecraft and needed to use it as a reference.
I suppose I could have more 'Steam' games but that would only be if I could be bothered registering humble indie bundle games in Steam, which I can't.