Melhelix: GOG also generally does a significant New Year's Sale, so that should only be 10 days away or so.
yyahoo: Actually, I can't recall a New Year's Sale at GOG. Although, up until last year, GOG's Holiday/Winter Sale used to last until past New Year's. The past couple years the sale has started earlier (no doubt to get a leg up on Steam) and so has ended earlier.
2014's New Year's Sale was the Time Machine sale, which worked similarly to the Insomnia Sale from 2013's November, except every purchase added time to the game up for offer. In the years before that, as you said, the Winter sale simply spanned the distance.
Edit: I also think in 2013 there was a start of the year sale at the beginning of January, but I could be mistaken.