I've just done this (I hate DRM, and thus got rid of my steam version) -- but I've just seen that there isn't a Mac version on GOG yet!
Is it coming soon, or have I done a terrible thing?
keep cool. all right. read that:
http://www.gog.com/forum/general/divinity_original_sin_on_gogcom_bstatus_updateb/page1 info 
We will release Divinity: Original Sin in the next few days. We are working on the Windows version of the game right now and waiting for the Mac build to arrive. The version of Divinity: Original Sin that will be available for sale, will be complete content-wise, and will allow for local/direct-IP multiplayer, but will come without the online matchmaking component and game auto-updating, which will be introduced as a later updates.
Mac version is coming - only needs time.
