There's a lot of experimentation going on in Google Reader. It feels like it's getting more energy than, say, Buggy Blogger (much less the Stuffed Sites).
Two to look at are Shared Items and Feed Bundles.
Shared Items aren't new, but they're getting more love. I don't know if this is new, but if you go to a Reader-generated post-share page (like mine) and you don't own the page or currently "follow" it, I think you'll see a button to "follow it".
I say think because I've only seen it once, and I clicked the button and now I "follow" that person's shared items. Following, as near as I can tell, is pretty much the same as subscribing to a feed though things you "follow" get are added to a special "follow" folder in. So this is a convenient way to add someone to your Reader "People you follow" section.
Feed bundles are a subset of the feeds that someone likes that are packaged and distributed separately from their primary feed. In Reader's "Browse for stuff" section you can find over 240 bundles from Google alone!