I think with a suspension or PNG they can block your IP or small groups of IP's from your ISP, but many SMF forums it sometimes comes down to the login/cookie etc so far as being able to view a bbs while logged out as a guest.
I think the punishment of not being able to use the bbs handle which other members are familiar with, good or bad, is the real punishment, as with today's tech, and VPNs being available for a few dollars a month, getting to "see" a bbs will always be possible if somebody wanted to try THAT hard. Like I said, that person's persona is still gone, and IMO that's the payment for a suspension. It's not like such a user could say "hi, my name is now JerkOff2000, but my old name was XXX", and get away with it for long without being told on. Persona, gone.