I'm lead admin on a popular mustang forum (link in my sig) and we run vB4 with no plans to change in the future. One of our competitors recently switched from vB to IPB (lolololol) and it was certainly not in their best interest, but oh well. Too bad for them.
I agree that vB5 is a piece of shit, but vB4 is still the leading choice for high traffic boards IMO. The CMS features on the vB4 publishing suite are really not that bad. We use it on our site and it's gone over well thus far with great reviews from our members.
So what is going to happen now for the rest of the FWS site? Run a separate CMS and bridge the two? That seldom goes over well. I'm sorry, but I just see this "upgrade" as another nail in the FWS coffin. I don't care what anybody says... I'm still a vB fanboy and I hate change, as do a lot of others.