Thanks Ron - do you mind expanding on #3 a bit?
Are you saying that all I have to do is change the site URL in the settings for the user's site from http://username.foonetwork.com to http://username.com (assuming they have the domain username.com registered and a domain pointer set in their hosting account to send it to http://username.foonetwork.com ?
Is that the idea or am I missing something? I can certainly manually edit the URLs of the sites for my users if this will work.