Just a real quick link to show that FriendFeed has added a "hide" feature that allows you to filter out specific messages, messages of a certain type for a specific user, or - better yet - messages from a specific service by any user.
I'm now using this to filter out Twitter messages, since I don't need to see those messages twice. Something that is undocumented is that this preference also trickles down to the API level. Meaning, of course, that Twhirl now also filters out Twitter messages from my friends on FriendFeed.
You can watch the video tutorial, by Ross one of the FriendFeed summer interns, to show you exactly how to do this. I'm really, really impressed with the way that FriendFeed team is building their product.