Thinking of moving from Apache to nginx

But I'm not sure how hard it would be to make the swap. Right now I use httpd.conf to hold my rewrite rules but otherwise know less about nginx and how easy it is to make vBSEO work. I'm trying to plan for the future while we're still growing so that I don't have to worry later on down the road.

Also, would there be any reason I shouldn't move to nginx (mainly vBSEO related issues but also other general issues that might occur).

I do not know exactly what the switch would entail, however nginx supports vBSEO, and we have rewrite rules. I would say as long as you get the vBulletin running fine on it, you wont have to worry about vBSEO.