in reply to Autogenerating usernames
One problem you may find with the wildly varying 'fallthrough' naming scheme is when users are trying to guess each other's username to send any kind of communication to them.
"Oh, I'm John Smith and I need to contact Bill Briggs.. they gave me J.Smith, so I guess he must be B.Briggs".
No, Mr.Briggs could have ended up with anything. Bill.Briggs, BriggsB, almost any combination of their name.
Whilst this does happen to some extent with normal 'JSmith, JSmith1, JSmith2' collision prevention it doesn't leave the user confused as to why their friend has this different name.