Two new features: resolved question sidebar (and feed) and RSS feeds for the Popular favorites page. All is explained within. [more inside]
New feature: RSS on all threads. If you're using IE7, Firefox, or Safari, open any thread on mefi, ask mefi, metatalk, music, or travel and you'll see a small RSS icon in your address bar. Click that, and you'll find a feed of the post and all comments. We'll soon add explicit links on the pages themselves, but for now the autodiscovery tag should work. Use this feature to track new comments on questions you've asked, threads you were interested in hearing followups, and any other thread you'd like to stay up to date on in your RSS reader.
alpha beta gamma whatever: MeFi Music. Built in 12 hours with help from pb, it's still got some rough edges and features to come, but for now you can upload a song you've written and recorded (this isn't for file sharing), stream it from the front page or from its own page (where you can also leave comments). You can add things to playlists and stream those too. And the RSS feed is a podcast you can drag into iTunes to suck down every mp3 that gets posted. I'm sure there are bugs and the color scheme was slapped together in five minutes, but expect to see things ironed out in the next couple weeks and I'll add it to the global nav for all sites when it feels complete. If you have any comments or questions, drop them here.
New feature: RSS feeds for tags on both mefi and ask mefi (example). Tag pages have links to feeds, or just add /rss to the URL to get the feed.
RSSdorkfilter: Here is a proposed RSS 2.0 feed complete with timestamps, tags, and author names added. Here's how it looks in bloglines. Is there anything missing for any app writers that use the feed? (paging Rothko...)
Google's new RSS reader might be pretty useful for following ask metafilter (screenshot). You can click the little star to mark a thread as a favorite.