I'm still real new to vBulletin. The only upgrade I've ever done to my forum is going from 3.8.3 to 3.8.4. I can only guess that vBulletin upgrading to a whole new number (vBulletin 4.0) is gong to be massive. Since this will be my first major vBulletin upgrade, should I expect a lot of the current mods/templates/skins I have installed on my forum to break when I upgrade to the yet-to-be-released vBulletin 4?
Go off of the articles and blogs about what the new structure and code is going to look like. You can find some in the articles section here on vbulletin.org, and you can find more on vbulletin.com