I think the idea with +1 is that it will eventually be the equivalent of the "add to memories" button on LJ, which additional functionality to learn what you interests are in order to better offer you things you might be interested in, whether it be ads or extending your network. It's also an "Aol!" signal, and right now it's being used primarily that way, judging by what I am seeing. The list of who has +1ed a post or comment is public, so you can follow a link back to see who liked it.