sanscript: Just a tip:
Unlike with STEAM, many of GOGs games can run fine without reinstalling them. Just copy over the folder with the game to a new Windows or computer install. Though, this might require you to either take the HDD out and connect it to a another computer, or boot up a live DVD/USB... but that's the beauty of being DRM-free!
Geralt_of_Rivia: Um, no. DRM-free doesn't mean portable.
Portable software doesn't need any external dependencies and can be copied that way. DRM-free just means that it does not have any form of copy protection that restricts your use of the software.
DRM-free software often needs to be installed because it requires external dependencies (Microsoft Visual C Runtime Libraries, DirectX, etc.), specific files in specific directories (config and save game in user directory) or even registry entries that are installed or created on install.
Of course, DRM-free doesn't free doesn't mean portable, and yes - many of GOGs games DO have a certain portability.
A program that is portable or not, in strictes sense, do need winlibs anyway so that isn't the only real def of being portable. I've doing this dance since the 80's and since these many of these games can be run WITHOUT being re-installed AND doesn't depend on 3. party sw like Steam games does, I count that as being a sort of portable.
If you look at portableaps.com many of these do require winlibs in one way or the other (the need for MS Visual, DX, Runtime etc doesn't count, practically every windows software need those in one way or the other)
Also, being portable doesn't necessary exclude the fact that it saves in another folder, but then again, we're basically having a discussion of semantics here ;)