I personally don't use FB but my wife does, and so do many millions more of people. It seems to me that the important things to watch are the viral impact that could occur because of a like button. I just went to CNN.com and looked at a random front page story. There were 58 likes/recommends to the story, meaning that 58 people had done the "tell-a-friend" routine with one click instead of filling out a form.
We as a species tend to form groups with similar interests. So this 'like' feature could get your page sent to a group with similar interests. If the president of the Red Widget club likes my page on Red Widgets, then the only outcome will be more traffic. It doesn't matter if I am on FB, but it seems like my site had better be.