You will be hard pressed to find php forums with the depth of modification as this or some of my others.
As for selective veiwability. it site owners descretion, and it leaves something for the members. its the whole point of coming to the sight to sign up, unless you are ashamed someone might find you there.
I'd go php, simply because of the enourmous amount of resources available, vbullitin is meant for people who dont know how to run a sight, as long as you have pockets for the license fees. But everyone has what they like, I choose php because of all thats availably for free, even though you have to do the modifications and some of which can take some time. Its a very reliable, highly customizable, has a widespread knowledgebase across the web. and aside from all that, it just plain works.