Quick note: the GOG download problem is due to invalid links on the GOG account page. Until this is fixed, the following links should allow GOG users (who have received and activated the codes supplied by Larian) to download the D:OS installer:

https://secure.gog.com/downlink/file/divinity_original_sin/en1installer1
https://secure.gog.com/downlink/file/divinity_original_sin/en1installer2
https://secure.gog.com/downlink/file/divinity_original_sin/en1installer3