FWIW

For any sites that are currently using a FACEBOOK authentication provider - to allow for login to a dnn site using a Facebook account.

 - make sure that you talk to your authentication module provider and obtain an update for your site BEFORE the 1st of October 2011.

Facebook are making yet another round of major changes to how their authentication systems operation
 - and as of 1st October any pretty much all older authenticationproviders that DONT use the facebook oAuth 2.0 authentication system will most likely cease to work.

Westa

If you need any tips or info - give me a shout - facebook auth can be a minefield - just dont know why they do things the way they do sometimes.  The big change this time around is in how the auth cookie is packaged and unpackaged - until now both facebook auth systems have been supported - but as of October 1 - only the oAuth 2.0 system will be supported.

Oh and just for hilarity - if you are using the FB:Login-Button xfbml system - the oAuth 2 requirements are not documented anywhere.

You know silly things like perms="" not being supported in the new version - and scope="" being needed instead.  Which pretty much breaks any older sites.
  
If you have not already discovered it http://facebooksdk.codeplex.com/ is a c# open source sdk for asp.net developers - that replaces the php sdk provided by facebook -  this sdk is a god send for asp.net developers.

Westa