AAAAAAAAllllllllllsooooooo................ 3rd party people can use your code and just replace the content with open source versions to make the same game and release that for free. Is someone really going to do it? Depends if it's a cool enough game, I suppose. It's almost like mods, but even with mods you still have buy the binary to run them where as with GPL'd code, someone just takes it, builds it, and off they go.

I don't like GPL very much, but I think it's worth it for Q3 if someone writes a better shader implementation and shadows etc..

BTW: GTKRadiant is $5,000 US to license from id Software for a commercial project, $10,000 if you want limited tech support. I know of one game in this community that's made over $10,000 with very little effort to get the word out and sell some copies, so, $5k for a good project seems pretty reasonable to me. Anyone wanna loan me $10 grand? I need the other $5 to hire some artists.