I guess my list of unplayed/hardly played games has grown since I've gotten Steam, what with their frequent sales.
There are only two games in my list that I haven't played at all since I bought them--Overlord 2 and Half Life 2: Episode 1--but that's because I was waiting until I finished the Overlord 1 and replayed Half Life 2 before moving on to the sequels.
I did make it through HL2 again without yet moving on to Episode 1, but I have not completed Overlord 1, and it's one of those games that I may never do so, simply because "I've moved on" since then. Not that the game was bad or anything.
Anyway, p3lb0x has a point. I often think to myself I shouldn't buy any more games until I finish all the ones I've purchased, but then comes along another Steam sale and something I've had my eye on (for years, perhaps) is only $5 and I can't resist buying it. Especially if it is multiplayer and I have a friend or family member who is also getting it.