I said I was going to do it, and I did it.
The forums are now running on SMF, with no loss of data. All passwords, posts, private messages, signatures, etc. are intact. The only problem I’ve noticed is that if you are initially unable to log in, you will need to delete your cookies from this site. On Firefox this would be Tools>Options>Show Cookies. Then in the search box put phpbb2asksteved_data and delete all cookies you see there. Or you could just Tools>Clear Private Data>Cookies. That should fix it.