The main reason I even started participating on Superuser.com is because a friend ripped me a new one for using phpBB. He said, "check out StackExchange, they have their act together!" I did, and it's true. So now, after learning phpBB and implementing the board (it's still new and in its infancy), I feel slightly regretful. I would love to use the Stack Exchange tool, but the cost will eventually be the main deterrent.
The attractive thing about phpBB is that it's free and open. However, I have heard that it lacks security. Has anyone had this experience, that phpBB is not secure, such that they changed board software? And, I wonder if Stack Exchange is going to introduce a cheaper option for low traffic users? Does this question belong on meta?