It would be cool to have RSS feeds on a per user basis. I'm thinking mainly posts but comments would be fine too. Something like http://www.metafilter.com/username.mefi/user/posts.rss and http://www.metafilter.com/username.mefi/user/comments.rss. It'd be a great way to keep up with people whose stuff you enjoy (like everyone's favorite) w/o getting lost in the volume.
How about a proper RSS 2.0 feed? The existing .91 feed doesn't provided authors or even datestamops. Also, the existing ATOM feed doesn't validate properly and doesn't work in the two RSS readers I use (NetNewsWire and Thunderbird).