It could also be or become a ranking/search quality signal in aggregate.

Google may also show aggregate +1's in their search results in the future (so social proof right in the search results):

>>And even if none of your friends are baristas or caffeine addicts, we may still show you how many people across the web have +1’d your local coffee shop.

http://googleblog.blogspot.com/2011/03/1s-right-recommendati...

>>For instance, your +1 could appear as part of an anonymous aggregated count of the people who have also +1’d the same thing

http://www.google.com/support/profiles/bin/static.py?hl=en&#...