Google released a new version of the Google Reader a couple of weeks ago and I've been using it for the last few days. I think that I've finally found a web-based RSS reader that I can live with now. I've wanted to move my RSS reading to a web reader so that I can access it anywhere, particularly on a mobile device. Google Reader in it's previous incarnations just didn't hit it right to me. The significant redesign they did really hit the usability issues right on the head.
If your looking for something a bit more sophisticated, and mobile, than the RSS functions of Thunderbird check out Reader. I don't think you'll be dissapointed.