I bought quite a few things on gog, the only time I ever really had a problem was that I bought fallout 1 on there and then they lost the license because the rights transferred over from Black Isle to Bethesda so there was like a six month period where I couldn't play that one game, but other than that gog is pretty good. Their client sucks but you don't have to use it.
I like the basic nature of their client as I just set the game to download and it installs it for me. Other than that I do not use it. To me it is like a download manager. I do like GOG and have a some games I got on GOG after getting them on Steam. Usually I waited for a good price to come along.