Believe it or not, vBulletin aren't so happy about vBTEAM's existance, even though vBTEAM does provide one place PirateReports can scour for URL's daily, and force those guys to pay out. In a way we're an asset to vBulletin.
I wouldn't upgrade right away after it comes out and is stable.
I'm an actual license holder of vB and the unrest in the official community forums is uncany, and not a single person has any faith in Internet Brands to actually release a good working copy of vB4 since all the main developers left.
I'd wait until atleast 4.0.2 before thinking of upgrading. Not to mention all modifications will need to be rewritten.