A lot of folks would like a memetracker for Google Reader (myself included), and if the big G's not going to provide one, it's up to third-party developers to attempt to build their own. One of the results has been ReadBurner, a service that tries to determine what items (not just feeds) are gaining in popularity at any given time based on the number of people sharing them on Google Reader.
Think of it like Del.icio.us, but instead of browser plug-ins or voting from the content originator's site, the system picks up on items automatically--that is, assuming people are clicking the little share button underneath a story in Reader. There's even an upcoming section for the items that aren't quite "front page" material but are picking up steam. The hope is that you'll be able to find some great, read-worthy content and keep an eye on the "pulse" of what people are sharing.
It's something Google could do a whole lot better if it harnessed every single publicly shared item and put them on a page. ReadBurner's solution it to gather its shared items from several hundred (hand-picked) influential Google Reader users in order to show what they think is noteworthy, similar to what TechMeme does with news stories.
In a chat with Mashable, developer Alexander Marktl noted that the site's in its very beginnings and open to change. If I could suggest anything it would be community inclusion--the option to add your own shared feed into the mix. Right now ReadBurner's working off its own list (which is currently down), that leans towards technology aficionados. It would be nice to be able to add your own to feel as if you're a part of it.