I'm thinking uof upograding our forum from vB3 to vB4 to take advantage of some new vB4 features. It's fairly large (10,000 members and 500,000 posts). Is vB4 stable and fast enough to make this a viable option?
I switched to VB4 too early, and I encountered a FaceBook Connect issue with a second-most-recent upgrade (if that feature is important to you) and haven't checked to see if the most recent upgrade fixed it. But if you have the time to re-skin your forums and you've verified that the mods and add-ons you deem essential are available, at this point I would say "go for it".
My forum has a similar number of posts to yours, and a lot more members.
i'm in the same boat as roger and am still waiting. one thing that puts me off is the number of updates released for vb4. i don't have many customisations, but still enough to make each upgrade annoying.