Vitek: Just checked. In 2008 there was no sale, in 2009 the sale lasted since the 21st December until the 3rd January, in 2010 it was 14th December to 3rd January and last year it was 12th December to 2nd January with the exception of Activision catalogue which ended on the 26th of December. So yeah, it is fairly certain that a sale will last past Christmas.
keremix: one problem is that wishlists might change during gog christmas promo
Ok, in that case what keremix suggested might not be much of a problem if the participants can restrain themselves until the gifting event is over, or only put those games on their wishlist that they don't intend to buy for themselves as soon as the holiday promo starts.
I don't have many games on my wishlist right now, but I'll consider participating and might eventually apply before the deadline is over, since choosing games for someone else sounds like fun. ;)
PCGameGuy: For those who have not yet tried it, the GOGWiki integration is very good here nowadays! If you sign up over there it can import your games lists and from here you can update your page with a simple click (at least I can in Chrome). I know my list is very likely to change in the next two weeks, GOG always does some cool stuff around the holidays that will either add to my list or get me to buy sooner! :)
Does the GOGWiki feature some kind of privacy options, like making your wishlist available for short time but keeping your shelf private or somethng like that?