There is now a version of Settlers on Facebook. I just started playing this game yesterday and will soon find out if it is a good or bad game.

Edit:

I played the game on Facebook for awhile and don't think the game is that good.

You can increase your population as much as possible without building a single farm. The farms are only used to reach goals such as producing a certain number of a crop.

The workshops also don't do anything. They are also just used to complete goals such as produce a certain number of some good.

They also copied the Zynga style of play so you have to beg your friends for certain things to complete a goal and spam the feed and piss off your friends.