This week, I had to create a few profiles (by hand) for Forms Auth user accounts. Of course, in order to do this, you need to make sure the SSP's People Picker can recognize them. I dutifully added the provider info and the requisite connection string to the SSP web.config, spun it up, and... nothing. It had no idea who these users were.
I tried saving the web.config file again. I tried restarting the IIS website and the app pool. I ran iisreset, and even rebooted the server. I added every MOSS account imaginable to the membership database as a DBO (just to be sure).
Still, nothing worked.
Finally -- in a fit of "this is so stupid that it can't possibly work but I have to try it" -- I went to Central Admin -> Application Management, extended the SSP application, and implemented FBA on the newly-created IIS website.
Lo and behold, the crazy thing started up again and recognized my users, and I could create a new profile based on a forms auth user from the membership database.
Maybe someday I'll investigate the why of this; for now, I'm just glad it works.