I think free forum hosts are great for those who are brand new to owning a forum. I've seen successful forums hosted on Proboards before as well, so there is a great chance that a free forum can be popular. However, most free forum hosts don't allow you to gain access to your database, so if you wanted to move you couldn't. Jcink is the only free forum host that allows you to make backups iirc, so you could always go with that. Have you ever made a forum using a free forum host? How successful was your forum?