I had a question in my head about whether or not Google would use the Facebook "like this" widget in their rankings. So I checked a page on CNN that had the "like this" stuff at the bottom. The code looked like this <span class="connect_widget_connected_text hidden_elem">You and 18 others recommend this.</span> which would seem to be a pretty easy thing for a Googlebot to read.
Do you want to test the basic presence of the widget, or the number of recommendations that it gathers? I would be wary of artificially boosting the count.
Since this isn't a link, any real effect would be in some area of the algo that we have no official information about. There is some conjecture around the SEO community that Google has developed an "social module" in their full algorithm that kicks in for just some verticals - some kinds of search taxonomy that they have defined.
If you want to test this, you would also have a challenge isolating this one factor, unless no new backlinks are showing up and no other changes are being made to your pages. And if people really do recommend the page, then it seems like some backlinks might be naturally popping up and disturbing the test.
So I'm a bit stymied on how to test around this factor.