My forum is PHPBB and Yes I have started with PHPBB!! Yet I am ranked on the first page for a lot of keywords!! Beating all the forums that run on VB and IPB that too older and more populated than mine!! So phpbb being non Search friendly is just an myth!! Believe me PHPBB is the best start available and the upgrade released yesterday has made it even better,
Just because you run a paid forum system won't make your forum any better ranked in a search engine... The thing is, if you use a forum system such as vB you are likely to slow your forum down >.< because this forum here (DP) is a prime example, its horribly slow, I mean it could just be a coincidence, but that would mean every vB forum I have ever used is a coincidence...