I am working on an ASP.NET MVC app using this library.
I have not used a whole lot of the functionality of the library since there are only two MVC specific class. An Controller Extension for getting a facebook api object, and an Action decorator attribute.
I have run into quite a bit of trouble with the methods in the Facebook.Rest.Data namespace.
Namely getting and setting Cookies.
Not sure what the deal is with this but it has been frustrating. And if it was not required by the client I would probably try and find a different library.