Navagon: I never use the default path to install games. I have a Games folder on a separate drive and they go in there. I don't understand why the industry continues to use such shitty practices when it comes to installing and running games. It's like they haven't learned anything at all since the DOS era.
Actually, most DOS games were perfectly happy installing pretty much wherever you tell them to, including directories that you can't delete and system directories.
It wasn't until Win 95 that developers started to get really stupid with things like that. MS deserves a great deal of credit for that by not providing an appropriate means of segregating and versioning DLLs from the start. And failing to provide appropriate user accounts.
I used to install things to a custom path, but I've given that up since so many of the software packages I've tried it with didn't like it. If I really feel the need to segregate, there's always Cameyo.
Irenaeus.: The Program Files directories are covered by UAC in Windows 7 and Vista, so installing there is a BAD idea if you're planning on using mods. I personally go for C:\Games, but each to their own. C:\Games has the advantage that it has no spaces in the title and is less than the DOS-limited 8 characters for names, useful for older games.
Which also means that if you get one that's infected with some sort of malware or poor coding practice that it's even easier to go from vulnerability to outright exploit.