I agree. I've mentioned this many times before but not by checking IP. I've been a victim of cookie theft and it was obviously not a pleasant experience though I happened to be on the board within minutes after my password was changed and i got into the FTP and renamed ultimatebb.cgi to .bak. That shut the board off in a hurry.
I would love to see something like this added to the core of UBB. I brought up having a second password that would be asked for after the UBB password was presented. I've settled for surfing the board as a non-admin (megamod) and in reality it is a good solution. There's really no reason I HAVE to be logged in as an admin all the time.
Anyway, back to the subject. I agree that this would be a good thing.