Ok, i'm not questioning that.
I have around 200 going on 250 (just got 3 more from here) and i can't do it.
Also keeping track may mean different things to different people.
Like i said, tell me the name of one game and i will tell you on the spot if i have it or not.
But ask me to sit down and put on paper a list of every game i have and i won't be able to.
Also, keeping track doesn't mean (to me, that is) just the games, but all the associated material that comes with it. Knowing what soundtracks, mods, maps, extractors, SDK's, editors, etc. i have for each game is a real chore.

All that might be slightly worse, but I think I could list all the games I owned, if I:
A. Had enough time.
or
B. Could be arsed.
For me it's all about being bothered to do it, and I don't see any life threatening situation where it could be necessary.

Well, i don't think i could do it regardless of how much time i had to do it.
And no, i also don't see any situation where i would have to do it, but that's not the point.
I want to be able to browse my collection DB and now what adventures+1st person+3d i have. Or what games released in 1997. Or what games i have from steam and what games i have form GOG. Or what hybrids i have in all genres. Or what games i rated above 9.0. It's the ability to retrieve this kind of info that interests me.

Hah, well, that. That would be a bit worse. Of course, I would be able to remember the genre, but release date, ratings and such would be worse.

Hmm, shouldn't be TOO hard to slap something together in Adobe AIR... sounds like an interesting challenge, I'll see what I can do (don't expect much).

And those are just examples, because you can factor in anything you want, provided you are willing to take the time to compliment the fetched info with your own tags.
It's a strange realization, but unlike everyhting else in my life, i'm quite the control freak when it comes to games :)
Thanks.
I appreciated, i really do. But the app i mentioned does all that already.
Before finding it i was also willing to take a whack at in with C# or something.
With my coding skills it would have taken me a year probably but that's another story :)

I use Delicious Library.
Pretty fun app, easy to use for "real" stuff (I pick a book, a game, a CD..., I "show" the bar code to the webcam, and it's done).
Oh, and visually, it's pretty close to the GOG collection manager, but that has been already said.

I AM Johnny Mnemonic. Problem solved :-D

It looks good but the $40 price tag and Mac OS X only aspects are a turn off.

Allow me to say sir that you have sucked balls in every single movie I've ever seen you in

It's less than a PS3 ou 360 game price, and it's very useful when you love to list all your stuff. Honestly, for what it does and mostly how fun it is to use it, it's a pretty fair price in my opinion.
As for Mac OSX only, well, it doesn't bother me... ^^ And I've heard that there were some equivalents for Windows, even if not as good.
BTW, there are some funny surprises in this app. When you "scan" a Star Wars product, you automaticaly hear the OSX intern digital voice saying "Luke, I am yout father".
As there is only one Johnny Mnemonic movie, he can not be so bad... just kidding.