I was tending toward vBulletin since this forum is so extremely cool! And I am thrilled that there is a hack to integrate it with my existing Mambo stuff.
Basically, I am wondering what to use for my Consulting Business site where I was thinking of creating forums for Clients about the projects I am working on... but if one client is angry about something (never happens, but...

) I don't want other clients to be seeing those threads.
I was considering that a good forum might mitigate a bugtracker system -- make the clients feel like they are participating in development rather than just yelling at me about bugs.
I don't know whether to use bugtracker (Mantis ?) or a Forum or both... and with my needs for groups and privileges vBulletin seems to be pretty extensive and it is feeling like I might need to use it exclusive of Mambo for my privileges needs(?).
But free is always a good thing

so I am looking at Simpleboard and others too.
I apologize that this is such an open ended "how should I run my business" kind of question, but matching the right technology to the problem kind of required I go into that squishy area.
Thanks in advance.
Brad