I was just about to implement it. I thought it was great. I thought anyone could vote for your content.
Well that is anyone with a Google account. If you don't have a Google account they require you to create one just to vote!
10% of my user population has a Google account. When you compare that to probably 80% having a Facebook account you will see why you might not see stats for a while.
Plus the button doesn't really look like a button. It looks like a badge. Unless you put text next to it saying to click it if you like this page, most folks I'm guessing are not going to realize it is a button associated with their Google account.
I've often wondered if individual sites put their own "like" or "+1" type button on a site if that would help with their own internal analytics as far as liking a page goes. The nice part is there would not be a requirement to log-in, sign-up or anything like that......Unless you wanted to have a simple pop-up to say something like "Name, City, State" or some sort of Captcha for verification.
Then one may be able to gather which visitors DO like the page without having to hand off that data to a second party. Now, one would have to wonder about "rogue" clicks, but I'm sure there's some way to filter those out.