Well, I decided to jump right into it. I'm now the happy owner of one vBulletin (owned) License. As soon as I receieve the license info on mail I will download and install the latest 3.5 release (RC1) as a test forum to play around with. Then when 3.5 or 3.5.1 final is released I will make a new install and import members from my UBB.threads database, etc...
phew, can't believe I really did it!