I'm confused by the Facebook registration process, so I know my users will be.
The "Register with Facebook" button is way down, so users will be halfway done with the normal signup process before they see it. Then, if you do use that option and you login via Facebook to populate the registration form, it just says, "You have registered." There are no further instructions on how to go to your admin area, or anything else. Just "You have registered," but no clue as to what to do next. (Most of our users are novices, so I'm looking at this from their point of view.)
However, even though the user is told that he or she has been registered, there is no new user and/or site in the network. So it appears that registration might not actually have happened.
UPDATE: Just for ha-ha's sake, I entered the Captcha code and hit "Register" a few more times. It finally said, "Thank you for registering. Proceed to main site." So, even though it had already told me that I had been registered, I had not. This is ultra-confusing. And, even after I figured it out, it was still confusing because it only gave the option to "Proceed to main site", which is the main site on the multisite network. Shouldn't it send you to the login for your newly-registered site?
Another issue is that the username seems to be assigned automatically based on the Facebook e-mail. So, since the username is also your subdomain, you end up with a very ugly site name like bobsmithyahoocom.ourdomwin.com.
Can this process be improved? Otherwise it's unusable for us.
BTW, I also can't get the admin "Login with Facebook" to work. It just redirects to the login page with %reauth added to the URL.