We are aware of that. :) Apparently Your (the community) help can speed up the process.
We plan on checking all of our games and than officially add "Windows 7 Compatibility" to our site. It might happen that some games will take longer than that to fix. Others might by impossible to fix. But do not despair - we'll keep you informed about what has been positively tested and verified as well as to what titles we cannot guarantee compatibility (lets hope that it won't happen) .
Only in case that you need the fixed version. Re-downloading your games with fixed compatibility with Win7 while you use XP/Vista will be pointless... Unless stated otherwise. :P You know how it is. :) We might coincidently fix something else - but again, we'll keep you updated.
One of the most interesting part of working at GOG.com is that we never say never. The only valid question is when do we say "now". ;) Linux / OS X definitely won't be supported for the time being but some things might change in the future. and we all know how it is with the future - future is unpredictable.
That will be a business decision. Maybe when Microsoft releases its next operating system (Windows 8 or some other catchy name) such decision will be made. But for now don't be surprised if our games continue to work on XP. :D