Around 300.
I often don't finish games. If they'll get boring I keep than installed for a few weeks. If still no interest of continueing after that I uninstall them.
A full .time job and a huge backlog means I probably won't return to those games.

I have yet about 500 games and still 350 to complete (meaning to me, seeing ending credits roll or a solid grip on the whole experience a game has to offer in case of 1000 Amps, Plants vs Zombies like games) or even start playing.. One game at a time, lately i'm trying to get off Morrowind and move on to Two Worlds II. Resident Evil : Darkside Chronicles Wii almost done and i want to finish Silent Bomber PsOne someday soon, but i recall this one is a baddy!

I used to have an account on Backloggery but CBA to manage it anymore when Darkadia does about the same with a better interface and a beautiful shelf presentation GOG style..

Link : http://darkadia.com/member/kwama57

How long is your backlog?

Infinite.

And what's on it?

Everything released between 1977 and 2012. And the games that I need to play and master again, too.

Ah, then chances are that you won't end up loving the game. I'm only a little bit further than you into it, and I'm quite enjoying it.