Now that I've used fav.or.it I'm not as enthousiastic about it as I hoped to be. Fav.or.it looks great: great look and feel, very user-friendly. It's also a very social feed reader (sharing tags, feeds, most-read posts, etc. etc.)! But it's still really in beta. You're not able to add your own feeds yet. You can only subscribe to predefined feeds.
What I was most curious about was replying to feeds right from your feed reader. But for some reason, this doesn't work. I tried replying to some posts. The reply did not end up on the blog that I replied to. I thought: maybe this takes a while. So I waited some. But still it don't show up. My reply also didn't end up in the '(my) conversations' section... (By the way, it would be nice if you could add your own feeds, because replying to a big blog just to test fav.or.it functionality is tricky... I'd rather test it on my own blog for instance.)
I'm not giving up though! I like the concept fav.or.it is showing and I'll keep following this reader.