I'll have a donate button up this evening then!

vBulletin is a more secure piece of software, and is a bit more resistant to spam attacks...thats the FIRST reason to upgrade.

Secondly, it has better group management and the ability to expand user capabilities a bit more.

Lastly, its paid for software, which means it includes support and warranties and whatnot (I haven't researched this).

A lot of the more "pro" level web communities I've been involved in are vBulletin forums, and I'm generally impressed with them. I wanted to make this site vBulletin to start with but didn't have the money to spend on something that might not have even worked out...now that its working out, its time to make it more pro.