How about grouping posts by topic?

I'd like to see google reader do something like google news's "...and
50 related from 10 other blogs on this topic" thing. I aggregate a lot
of blogs that like to discuss the same stuff, and it gets tiresome to
wade through 50 posts before coming to one that's on a different
subject. I'd like every item in the bar at left to be on a different
topic, and I should be able to expand the item in place to see other
posts on that subject.