There are now multiple feeds and this comment describes how to find them: https://www.lesserwrong.com/posts/Zo462cTMBYsc45foA/rss-feeds-are-fixed-and-should-be-properly-functional-this#tW36qT9DSq6pgJwsf
Took me a while to find this so i'm sharing in case anyone else is puzzled like i was. This should be a feed of all lesserwrong posts: http://lesserwrong.com/feed.xml