We used to have a custom dedicated page collecting the RSS links to sub-forums.
This page vanished with the last big forums software upgrade. You can directly subscribe if you use Firefox, but not all of us do.
A dedicated page may come back one day, but all custom work is a pain when upgrading. So, in the meantime, you can use this url for individual sub-forums (the forumids is ABT’s, you find it in the url of each sub-forum)
http://ubuntuforums.org/external.php?forumids=326
And this one for the whole gear:
http://ubuntuforums.org/external.php
