There's an option to be notified whenever someone replies after you in a discussion board post, but I don't see a way to be notified for new discussions. To me, this severely limits the use of facebook groups/pages as a forum for discussion, since you have to check each page individually.
Either email or rss/atom would be good. Even a page on facebook which showed new discussions in all of the groups I'm a member of would be okay.
Best Answer
Facebook has updated their Groups allowing this feature. This does not work for old groups though only newly created groups.
The settings for new groups can be seen in the upper right of that group page.
![alt text](https://i.stack.imgur.com/Tkck3.png)