There are several community oriented sites out there which can, when requested, search through an address book (either online or using Outlook, etc.) and other social media sites (such as FaceBook, LinkedIn, Twitter, etc.) to make suggestions as to people the user would like to connect to. Basically, it checks the address book against the existing member list and flags those that are in both lists.
Garmin Connect is attempting to become a more social site. As such, it should have such a functionality. (If it's there, I can't find it.)
Additionally, it should allow for sharing of items as requested on other social media sites. The most obvious is badges, but new records, etc., should also be sharable. (On the other hand, you probably shouldn't set up automatic sharing of every run. That's a form of social media spam.)