I am also very interested in this mode on a 3.8.5 even if Facebook drops, but from reading the thread seems is not that stable, or did I get it wrong?
Here is working fine with facebook and gmail (i have test it)
I have many users not so handy with computers so this type of registering is much easier for them (not all people make forums for IT users

).
Will keep an eye on this one and read more pages.
Imho this modification should be standard integration in VB. Is all about making much easier for users to get in from other networks or services.
Keeping them is other story ... but who to keep