The "other customers also bought" section would be an excellent tool, allowing people to find similar games, or completely different games that people with similar tastes enjoyed. Unfortunately it doesn't appear to work properly.
With virtually every game I look at, the list always says:
Fallout
Fallout 2
Freespace 2
then 2 others (usually Lure of the Temptress and Giants: Citizen Kabuto).
I expect that this is because these games are by far the most heavily and widely bought, and thus the algorithm that calculates this section weights them heavily. Certainly, once the purchasing patterns settle down and even out somewhat, we may get a more diverse "Other customers..." list, but right now, it just isn't working.
Is there any way that this could be solved? 90% of the site works fantastically, and it is a shame that this one piece is currently useless. Possibly adding a variable to the algorithm that more heavily weights similar genre titles? I'm sure there's a hundred and one great ideas out there.

The Fallout games have been on the top of the best seller list for quite some time. Ive been here since the close beta and now its when there are other games at the top more frequently.

Actually, I would say that it is working perfectly, since almost everyone (except me) bought the Fallout games when GOG launched. I'm guessing here, but I don't think the "algorithm" is really all that complicated, nor should it be. It probably just looks at the member accounts of everyone else who bought that game and gives you a listing of the top 5 most frequently found titles in those libraries. The idea is not to show you similar games, the idea is to show other games that you might find as enjoyable as the game you are currently looking at, regardless of genre. It is based on the assumption that you might have similar tastes to everyone else who bought that game.
The only thing I think should be "fixed" would be the exclusion of the free games, Beneath a Steel Sky and Lure of the Temptress. Considering they are free, I'm sure some people just said "Free game? I'll take it!" but don't actually play it (like me). If BASS or LOTT had been paid games, I would never have got them myself.

I understand what you are saying, but i disagree in the purpose of the tool.
Right now it is simply acting as a 'most bought games' link, where it should be a "you liked that, so we think you will also like this" link.
There's obviously a place for a 'most popular' list, but a "similar tastes" list or something like that would be far more useful on each individual game page.

Assuming that I am correct about how it determines what to put on the list, it sort of is a "you liked it so we think you'll also like this" list, not just a "top sellers" list. If those games are the most purchased games by other people who also bought the game you are interested in, doesn't that indicate (roughly) that the majority of people who liked that game also liked the top seller? Of course, it could also be a bit of a self-fulfilling prophecy like the top 10 on the wishlist, i.e. Fallout stays at the top seller spot because it is the first thing everyone sees on the list, just like System Shock 2 on the wishlist.
Regardless, I think it will "self-correct" itself as GOG expands and more people start buying from it. Remember, GOG is still in beta, so it has a long way to go yet. By next year, there could be a completely different set of games listed next to whatever game you are checking out today.

Well, the name says it all, really. "Other customers also bought" means "these are the games that other customers who bought this game also bought". What you're talking about is a "Recommended for you" function, which usually works as you described. But it's a different function. They shouldn't call it one and let it work like the other.

I agree with durns. The purpose of such a list is usually to show what other customers >>LIKE YOU<< have bought. It's not a huge problem, but I think it's something that GoG should add to their tracker for later fixing.

Fine, but if they change the function, they need to change the name too. Otherwise, it's misleading.

Maybe "You might be interested in..." for the global list. "And people who bought this game also bought..." for the one on the game description page?
As it stands now it's even more misleading. Top sellers would be a correct title for that.

Not if it's actually only looking at others who've also bought the same game.

But it isn't.

Actually it is. The listing that appears on each game's individual page is showing the games that were also bought by people who bought that game. If it didn't, then every game would be showing the same exact list, and they are not. The only common game seems to be Fallout, which clearly nearly everyone here has bought.

Uh... actually, it displays the same list for me on any title. Always excluding the current title of course. ???

For Colin McRae Rally 2005, the top of the list is Toca Race Driver 3.

Just as an example, I took a look at a few of the games on the main page of the catalog:
1NSANE: Fallout, Fallout 2, Descent + Descent 2, TOCA Race Driver 3, Fallout Tactics
F/A-18E Super Hornet: Fallout, Fallout 2, Descent + Descent 2, Fallout Tactics, Descent 3 + Expansion
Hostile Waters: Antaeus Rising: Fallout 2, Fallout, Sacrifice, Fallout Tactics, Perimeter
Perimeter: Fallout 2, Fallout, Sacrifice, Fallout Tactics, Hostile Waters: Antaeus Rising
Stronghold Crusader: Nothing. Apparently no one has bought this game.
Painkiller: Fallout, Fallout 2, Sacrifice, Fallout Tactics, Earthworm Jim 1 + 2
Panzer Elite: Fallout, Fallout 2, Arx Fatalis, Sacrifice, Descent 3 + Expansion
In Cold Blood: Fallout, Fallout 2, Fallout Tactics, Broken Sword 2, Broken Sword 3
Note that Fallout 1 and 2 are always listed (though not always in the same order), while the other games on the list are pretty much random and in a few cases, appropriately similar.