For the sake of transparency I should note that I am one of the creators of Forum Generator.
With regard to phpBB's performance in search engines, a few weeks ago I created a step-by-step installation guide for the phpBB SEO pre-mod which offers effective URL rewriting (topic titles and forum titles) as well as RSS feeds and XML sitemaps. The mod plays with FG very well and spiders stick around longer than they do with just a conventional, vanilla phpBB installation.
We opted for phpBB over vBulletin *initially* because phpBB is free, which means that we wouldn't be supporting people pirating vB which would be the inevitable outcome considering a large chunk of the demographic that purchase our tools. There is also the added advantage that it is very easy to explain to the inexperienced how to install phpBB with the seemingly ubiquitous cPanel plug-in Fantastico.
There will be a new beta available to customers in the very near future that integrates the last 4 months of customer suggestions along with new content sources and features. This application is still being actively developed and we take support and suggestions very seriously.
There are quite a few reviews on one forum in particular, but I don't want to link to it because I don't want to break WF forum rules. Feel free to PM me if you have any questions and I hope this message hasn't come off as too gratuitous.
