Your math is unassailable.

Not a very impressive promo, I'll stick to the regular weekend deals.

I wonder if weekend promo adds up with this?

I mean, If i buy two games that are on 50% discount, will I get extra 10% ?

Nope. The OP says,

"P.S. When you buy games at GOG.com you always receive the highest advertised discount, but our promos don’t stack. So, if you buy any game on sale for more than 10% off you will receive the higher discount instead of this one, and it won’t count towards our “buy two games and save 10%” special."

Main posts are always tl;dr for me, sorry :P

10% is really not much, but better then nothing. Sadly, this not enough for me right now. :(
Anyway why 10? Why not 14? (Because it's Valentine1s Day) or buy one, get one so your game won't be lonely. :)

Nice. I bought 7 games. Yesterday.

Bah.. If you actually read the forums you would know we're not all nice to our games - some of us have huge backlogs of games collecting digital dust, unplayed, unloved , in the dark, forgotten. Some of us even have a sadistic streak, installing games, and then just ignoring them until we one day uninstall them, without even having played them.

My GOG games have been mistreated so badly that they've started praying to higher powers to let the bad sectors take them away, bit by bit, in to oblivion and final peace. Currently they're all confined to a separate partition that is unmounted most of the time. The only happy game I have is Sanitarium. It feels safe and at home there, if not loved.

But what do you decide to do, knowing this is happening to your games, your labour of love? Run yet another promo that will ensure even more games will be suffering this fate, that's what. This isn't a two wrongs make one right kind of situation - on the contrary, it's one right turned into almost two wrongs. Luckily for you I'm a "ludiciopath" and thus support you whole-heartedly.

I have decided to doom two games to the uncertain fate of unregulated, no unions allowed, all sales final, privately held ownership. That is, one of you may get your grubby hands on "Evil Genius" and one other GOG game of your choice (except those on sale now, including TW2), for you to add to your backlog and let them stay there and rot for as long as you like.

There are some conditions, of course:
1. You must have a backlog of GOG games of at least three titles. List them (3 or more) in your reply.
2. You do not already own Evil Genius. If you don't own it because you don't think you'll ever want to play it, even better.
3. You must be able to define "ludiciopath" convincingly.

The first to fulfill all three conditions will be the winner.

+1 for Evil Genius (which I already own) I'm going to answer your questions anyway because I want to:

1. I have a large backlog that includes: the Little Big Adventure games, Flatout, and Rayman Forever
2. I already have Evil Genius and it sits in my backlog looking at me, evilly.
3. A ludiciopath is someone who is obsessed with the rapper Ludacris and has an infatuation with fried chicken and big butts.

Eh, 10% is kind of underwhelming. Especially when you consider how cheap the games already are.

1. Witcher, Broken Sword and Empire Earth have yet to even be downloaded.
2. Every now and then I look at Evil Genius and think hmm, I might like that. An hour later and I forgot it even exists.
3. A lucidiopath is someone who have gone compltely mad in their efforts to have a clear perception of the world.

Weak promo.

1. I got Broken Sword 1-4 in my backlog too, as well as Empire Earth 1-3 (although I may have actually played these for a bit; I just can't remember it). +1 for Witcher, though - it says "hardcore backlogger" loud and clear.

2. You probably will like Evil Genius. If you ever play it. I suggest using the wishlist function - if nothing else, the games added there will get their hopes up; only to be brutally and unceremoniously removed on a whim later on when you're spring cleaning your wishlist.

3. Not bad - quite convincing - but unfortunately, wrong word. (Feel free to try again)

How embarassing.