I doubt they will publish any numbers on this, but they seem to be doing fine at the moment. Regardless of that, it's always recommended to download the games in your account and store them somewhere safe for yourself. Since the installers are DRM-free and therefor independent of GOG's servers, that way you will keep your games no matter what happens to GOG, which is GOG's biggest advantage over services that make the availability of most games dependent on the access to your account.
Post edited October 27, 2014 by Leroux