Ajax Blog wrote about a few AJAX-powered feed readers.  Here are my reviews:

Inform is annoying from the get-go because it opens a popup window from its main site.  Not cool.  It seems to be kind of difficult to use and unnecessarily complicated (read software bloat). 
My rating:  1/5 stars

Orangoo looks like a great idea, but it's not quite up to par.  It has a bunch of errors and problems, and it's painfully slow.  I'll wait for version 2.0. 
My rating:  1/5 stars

Rojo is pretty cool.  It has the ability to tag and share stories with other people.  It's a lot like a social [insert buzzword] site, such as Flickr and del.icio.us.  Its only downside is that it seems a little slow and it's slightly hard to navigate through. 
My rating:  4/5 stars