I currently have $11 worth of my $30ish still installed, one being $10 Beejive that I bought yesterday, the other being Flight Control, best game and only $1.
The question of what's still installed is a fair one... I don't keep games installed after I haven't been playing them for a while, particularly because I have an 8GB model.

Of my games...
Rolando - did not finish, not installed (need to put it back on and finish it)
Spore - finished, uninstalled
Brothers in Arms - finished, uninstalled
Hero of Sparta - finished, uninstalled
Ferrari GT - finished, uninstalled
Castle of Magic - currently installed, currently playing
Toy Bot Diaries 1-3 - finished / uninstalled #1, #2-3 not on there now but haven't played them yet
Bobby Carrot - $7.99 - currently installed but not playing much, about 2/3 done
iDracula - currently installed, felt I got a good play out of it, don't play it much now.