Way too many that I care count. Enough for four life times at least.
That being said, I don't count every game I own as part of my backlog, only those I actually desire to play and beat. As I try to tell myself, being a collector doesn't have to mean actually playing everything you have. Like, I have the whole Devil May Cry trilogy on PS2, but I ain't ever gonna beat 2.
Collecting something and not using it may sound strange to some, but sometimes you just collect games, movies, books etc for the artwork or whatever. Not saying that's what I do, but to return to my previous point I also have hundreds of DVDs... ain't ever gonna watch 'em all.