I recommend you use BuddyPress – there are a lot of great plugins that will make it exactly what you need. Parallelus uses BuddyPress forums and it works fantastically.
BuddyPress for forums??? Or, is it bbPress?We use phpBB3 (bbPress 2.0 was not ready when we started our support forum). It also works fantastically for us and our buyers are happy…
I do use BuddyPress and group forums (not bbPress site wide) for my theme support. It actually works great because I’m able to make each group private and with a plugin I made it auto-validates the purchase before users can join a group. I like this structure because it keeps the support organized for each theme independently and verifies the purchase of each item, like having a forum for every theme but under one site.
One difficulty was getting BP forums to support posting code. I had to do some tweaking for that but bbPress already does this. Also, the BP search is junk. It won’t return results from private groups unless you hack the plugin and it only searches the title (and tags I think) of forum topics. None of the content is included in the search. I ended up adding a PHP search engine on my server which crawls the site and then integrates into WordPress with some backend requests. It was a bit difficult to do but it lets me search all of the private forums and index the full content of the page. It still needs some tweaking but performs very well overall.
I probably would not have gone this way except I wanted to make use of one of my own themes and already had all the BP work done for two of them. I used my Salutaton theme and it worked great after making these updates.