According to the buzzfeed article, the feature was pulled from a discontinued project called Google Sets. So yeah, sounds like they had a cool feature built that is no longer getting updated and they decided to toss it in to google docs.

http://www.buzzfeed.com/justinesharrock/a-glimpse-into-googl...

I personally think this is awesome.

EDIT: ahh, sorry. Just saw the other comment that points out Google Sets. Anyway, this is really cool, playing around with it now, when I should be working.