When Facebook gaming giant Zynga bought Newtoy and rebranded it as Zynga with Friends, it was only a matter of time until games from the "with Friends" franchise started popping up on Facebook. Sure enough, Words with Friends is now playable on Facebook as of a couple weeks ago. The game's interface is basically identical to the iOS games, so if you're already familiar with those, you won't need to adapt much to the Facebook game.
The coolest feature by far is the game's integration with the mobile versions. Playing the browser-based version will sync game progress to Words with Friends on iPhone and iPad pretty much instantaneously if you have the app synced up with your Facebook account. You can start a game on Facebook, then pick it up later in the iPad app. It's all very easy to set up.
Words with Friends on iPad has almost exactly the same interface
Unlike many other Facebook games, Words with Friends does not appear to require Flash, which is a definite bonus if you're playing the game on a MacBook. My wife is a Zuma addict, and I can always tell when she's playing because it sounds like she's got a jet engine in her lap. Words with Friends doesn't spin up the fans at all, and it runs quite smoothly on her Mac.
Words with Friends is free to play on Facebook, and there are free versions the iOS apps, including the HD version for the iPad. So if you've been curious to try the game, now's your chance to get in on the fun.