You'll have to redownload the game every few weeks and see if the file is different from before. Use a program like HashCalc or WinMD5 on both files and see if the results are the same - if different, the file has changed and you can throw away the old one (and install the new to see what has changed), if the result is the same you can throw away either installer because they're the same.
You could also wait until GOG announces that all games are fully Win7 compatible and then redownload all of them, at least you'll know that all your downloads do work as they should, though some of them may have worked before as well.

Gothic 1 doesn't work for me in Win 7. It won't even load on startup. Has anyone got it working yet?

Well they say, that it works fine on ATI cards. It's unfortunately unplayable with nvidia, but I can load a game and even play it - however with really terrible game performance due to some graphics (texture?) bugs caused by Win 7 nvidia drivers :( Same for Gothic 2.

Personal nightmare and realms of arkania 3 worked fine and both register in games explorer for me (windows 7 pro 32bit)

yeah i have nvidia, it won't even start up. bummer.

Buy an ATI card and it works perfectly. ;)
One temporary fix is to roll back your driver to the last version that worked with it (the version is described in one of the threads), but if you have a very new-model card those older drivers won't support it. I don't imagine Nvidia cares about fixing this, so hopefully GOG/PB can throw together some sort of fix.
EDIT: also note that Gothic II reportedly has similar problems on Nvidia cards (which is not surprising since it shares the same engine), but once again ATI cards run it just fine.

Didn't see it in the thread but Under A Killing Moon seems to work fine under Win 7. I'm on day three with no problems other then occasional sound glitches, which if I remember right have been there since the beginning.

Stronghold work perfect in Win 7/64 bit

Blake stone series
duke nukem: MP
Rise of the triad
shogo
all run in windows 7 64 bit

Windows 7 - Ultimate (32-bit)
Settlers 2 : Gold >> (Installed as Admin (proper, with full controls/access)) - registered in Game Explorer. Causes slight issue with resolution/colour depth, but acceptable, and works fine.
Fallout >> (Installed as Admin (proper, with full controls/access)) - Installs properly, runs as normal (though seems jerky and slow with the hi-res patch/mod) but gets "Unspecified" in Games Explorer...and can't be clicked there, or moved, or anything... will have to mess with that to see if I can get it running from Game Explorer.
Dragged the game exe to Game Explorer from install Dir, and it asks for a CD??! O_o
Fixed the "lag" in game-play - reinitialised the hi-res patch.
Commandos Ammo Pack >> (Installed as Admin (proper, with full controls/access)) - works fine, as is.
will try more later...

Advent Rising worked on Win7 pro 64 bit.
Only issue is that it sometimes crashes right before a cut scene. don't know if that is os related or not.

Still on W7 Ultimate 32-bit :
Darkstar One - works perfectly. ^_^

Win7 Ultimate 64 bit.
-Riven
-Myst ME
Both are working fine. Installed both as admin and also run both as admin. Zero problems so far.

I get the same issue with the sound under Windows 7 Ultimate 64-bit. However, the sound works perfectly in Windows XP Professional 64-bit running on the same hardware. The Pandora Directive has the same issue, too.

Running on a win7 Home, nvidia GT130M
Septerra Core: seems to work without problems.
Sacred Gold: installs and is "playable", but lags like hell - the lag can be helped a bit but not eliminated entirely.
Ground Control II: installs and is playable, but videos are glitching and I need to start the game twice every time, and first startup seems to claim some cpu - even though the game doesn't seem to be running (checked job list) - which entails a quite heavy burden on the pc.