I write a lot about Facebook as more than an acquisition tool - it's a conversions tool, particularly through registration and activation. I bill it the "progressive registration" (read more here). Here is a terrific example from Vacationist. First, the registration box is done in a visually clever way: it hangs atop the background image and has six key fields (First Name, Last Name, etc). When the Facebook Connect button is clicked, the fields change, are all prepopulated except for zip code and the title changes from "Become a Vacationist today" to "Register with Facebook". All that is required to do is enter a zip code and press Register.
One other interesting piece: if I had any Facebook friends on Vacationist, they would appear directly next to the register button. Right now it just says "0 friends" (probably better to hide that!).