Social network and mail logins

For only a short time I’ve been looking I into integrate logins for my wordpress (multi)site, because I would like some interaction between my site and Facebook. I see there’s a myriad of resources but haven’t seen too many documented problems–the only one I’ve seen is that some workplaces might block Facebook related pages or logins, and that’s not really a problem for me anyway.

There seem to be a lot of options and mostly all integrated together anyway, but am curious as to whether there is any negative feedback on these?

What has/have/had any user experiences been with these logins and especially want to hear about any problems. Thanks