Most of the people use the Facebook event page to show if they will attend on a DUG or not.
I think it would be great to display this information in a drupal event node.

I'v found a module which was developed for this: http://drupal.org/project/fb_event
(But actually it is not working for me. I'v tried with the 7.x-1.0, the 7.x-1.x-dev versions, and with git clone too. I know that this module is not really in active developement.)

If somebody else is interesting about this feature, maybe we should have to work on it...