Sharing articles was a built-in option in Google Reader for as long as I remember, and I've been using the app since the summer of 2006. It started to evolve and become more social about a year ago, but the feature didn't became very popular until the acquisition by Facebook brought a big cloud of incertitude over the future of FriendFeed. It also helped that Google Reader eased the access to the shared items by giving them an easily readable address, that can also be added to Google Profiles.
One of the nice touches in Google Reader (and other Google apps) are the keyboard shortcuts. I use them often to navigate between subscriptions, especially since I only display the updated ones. The other day, when reading through new shared items, I realized I never used keyboard shortcuts to access the items shared by individual people. Immediately I wanted to post a suggestion for this on the page for "Product ideas". Of course, I quickly realized this feature already existed, by using the all-useful help shortcut '?':
|g then f:||open friend selector|
|g then <Shift> + f:||go to friends' shared items|
|g then c:||go to comment view|
I find the first one to be the most useful: you get a list of people you have subscribed to, that you can easily navigate and filter by typing the first letters from their names. Here you can also access the "People you follow". The overlay dims the friends that have no unread items, like the subscriptions selector. But unlike subscriptions, the people you follow are not sorted alphabetically, but most likely by 'recency'. This doesn't seem to be influenced by the options you can change in the drop-down menu from the tiny arrow in the sidebar.
It's a little odd that this pop-up displays the friends only on the right side, while leaving the left side completely blank. It's not the same as the selector for subscriptions, it uses all the space available. Since it's the same across all the Windows browsers I use (pretty much all the big names), it's probably a small bug.
I also noticed that the shortcuts for navigating to the next/previous subscription (<Shift> + n/p) completely ignore the friends area. Google Reader probably treats feeds and friends is different ways internally, since they also have a different set of keyboard shortcuts. I think it would be easier to navigate Google Reader if these two were integrated, i.e. have a single selector for all subscriptions and the same set of shortcuts for navigation. What do you think?