I think the reality of how +1 will be used will be more like this: you see your list of search results. The first three are so-so and the fourth one is great. You think to yourself "why the hell was the great result not at the top?" and then click the +1 button to promote it. Google uses this info as a signal, both globally and for your circle of friends.

I think it could work, as long as it's not gamed into uselessness.