Total of .... 4 (though one is not really an install)
WoW (though not subbed as I've been busy moving house)
Warhammer (never subbed after the free month but live in hope it might be one I want to play again)
DDO (trying it out for a while now it's gone free)
Free Realms (though this is just a browser thingie)

Made the mistake once of uninstalling WoW and ever since having to go through the pain of re-installing and then patching, I'll only uninstall if a game is NEVER going to ever be played again.