And they're taking advantage of it in droves. Luckily for Facebook users, many of these games are mighty fun. Take a look at our 10 top picks for getting your Facebook game on.
10. Biotronic
Offering a biotechnological twist on the puzzle game genre, Biotronic features easy mouse controls, exploding combos and artful animations.
9. Restaurant City
From popular casual games developer Playfish Games, Restaurant City continues in the venerable tradition of casual games like Diner Dash. Combining elements of time management games and virtual sims, in Restaurant City you start your own food joint, customize it, and vie against other restaurants to become the talk of the town.
8. MindJolt Games
Actually a collection of various titles, MindJolt Games includes a number of arcade, puzzle, strategy and sports games to play solo or in challenges with friends.
7. Know-It-All Trivia
This one's for trivia buffs: Know-It-All Trivia pits you against your Facebook friends to test your knowledge and show off the size of that big brain of yours.
6. Zynga Poker
It's hard to argue with at current count over 18 million active monthly players. If you're already a Texas HoldEm fan, Zynga Poker is probably a no-brainer. If you're a card enthusiast looking for something fun to pick up on Facebook, you're in good company here.
5. Bejeweled Blitz
Insanely addictive on almost any platform, this gem-swapping puzzle title comes from the highly regarded house of PopCap Games.
4. YoVille
Zynga's YoVille is a Sims-like virtual world on Facebook. You start off with your own apartment and do virtual "work" to get the money to decorate it. You can visit your friends' virtual homes and chat with them in real-time.
3. Mafia Wars
Priding itself on being the "#1 Crime game for Facebook," Mafia Wars has over 25 million Facebook users doing crime jobs for cash, vying for respect and fighting to be the ruling family in fictional New York.
2. Word Challenge
Here's one for the wordsmiths and language lovers out there. In Word Challenge, you're given 6 letters and need to generate as many 3-6 letter words from them as quickly as possible. If you like word games like Boggle or Wordle, you'll love Word Challenge.
1. Farmville
With 11 million daily players and counting, Farmville is a virtual force to be reckoned with. If you like management-type games where you build and monitor assets -- or if you just love farm animals -- this could be the Facebook game for you.