Google Reader recently launched sharing, a feature that I had a hand in. I've used it to power my link blog, available in the sidebar (only on the front page). Although these sharing "clips" are easiest to use when pre-styled with one of our color schemes, you can choose the "None" option and then use your own CSS to make them blend in with the rest of your site, as I've done. And since it's all JSON underneath, you really use a public label any way you want on your site.

What may not be obvious about this sharing feature is that it can be used together to splice feeds. Furthermore, you can chain shared labels. For example, the "Stuff written (or recommended) by the Reader team" section in the Google Reader blog was put together like this (arrows indicate subscriptions/labels being applied):

This way, everyone gets to control their own "me" label, without having to modify the team account when wanting to add/remove feeds.

While developing this sharing feature, it became clear that the ultimate origin of an item in a feed is very important (i.e. I may see it because I'm subscribed to your "web-dev" label, but really it's from QuirksBlog). We joked about the need for a "Molecule" format that would specify the aggregation of multiple Atom feeds. We even began coding a (namespaced) origin element that would contain the title, id, homepage URL, etc. of the originating site for this item. Then, while re-reading RFC 4287 for another reason, we came across the source element in Atom, which does exactly what we had set out to (re)implement. This tells you two things:

1. The Atom people were pretty clever to have foreseen this use case.
2. No matter how well your spec/documentation is written, people will still miss things (a.k.a. everyone is a bozo at some point).

Now that we produce feeds for others to consume, it's nice to use Atom to its fullest so that we can validate (there are some scary looking warnings that we'd like to fix, but as of now that feed is in fact valid Atom 1.0).