Only problem (and for me it's not) is most the information does not populate, you get a username and that's about it. No e-mail but it does't matter for my needs.
Other thoughts: The plug-in gets the "log-in with Facebook" image directly from Facebook, and for some reason there is a small white space below the image. On a light colored page this would not be noticeable but on my dark page I see it. Purely cosmetic and I'm not complaining.