I am working on an implementation of Facebook Connect on this blog. I am working on a longer post but for you who argue that Facbook Connect is something complicated should have a look at this tutorial. For WordPress there are many plugins as well that you can find here.
Only use these plugins. The ones that are not listed on this website but are available through WordPress.org are generally 50% not updated to their full extent.
But if you build from the ground on up that I will do with my new blog I suggest you put this blog in your RSS-reader and keep reading. But first this video.