We have feeds for all the public forums @ www.asp.net/forums now. For example, you can grab the announcements feed here.

Just look for the familiar at the bottom of the page when viewing the threads in a forum.

You can filter the list of threads returned by a forumid parameter or a count parameter on the querystring of the rss.aspx page. For example:

http://www.asp.net/Forums/rss.aspx?forumid=11
Returns most recent 25 threads in the Announcements forum

http://www.asp.net/Forums/rss.aspx?forumid=11&count=50
Retuns the most recent 50 threads in the Announcements forum