The other issue that I see here is the culture that is present. Think of everyone that uses google - do you want all of their votes to influence the content that you see? I don't want to see the eggplant tofurduken recipe that Aunt Millie +1'd. Sure, you can limit the influence to just your circle of friends, but that doesn't bring much new to the table. Reddit has done well because it allows for this context of culture to be one of it's primary features (via subreddits). Even HN has this driving niche focus sitewide.
All that said, while I dont expect this to take off, I do expect to see a "+1 THIS!" button next to the "tweet this!"/"digg this!"/"reddit this!" button on every blogspam post out there.