to phpBB is really fun..
Vbb - About 250us
phpBB - free.
I have probably more features then this forum has here and probably more secure too. But then again I tweak about 8 hours a day to customize my forum where as David may not. Thats all preference..
phpBB has been known to be more secure than Vbb many times. Mainly because it's an open source bulletin board, Thus it's also more prone to attack because of it's open source. But with the right security features inplace I have a secure place.
Dont get me wrong, I like Vbb. But I'm not willing to shell out the money when I can do the same stuff for free.. Heck You want Vbb,,, No problem you can easily convert phpbb to Vbb face and attitude for free. With all the functions too..
But back to the orginal problem at hand.. PM popups are a great notification, and doesn't use them much resource.