I'm pondering upgrading my site tonight with a design that's been in the works since February. I've been up until 3 AM the past few days working on the development server and talking to my beta testers. Convince me not to do it.
My list just off the top of my head:
Close forums
Transfer plugins
Transfer files
Run upgrade scripts
Update wdf_definitions for forumids, etc.
Add FAQ items
Add a couple phrases
Rebuild WDF Notifier to point to proper server
Update vB settings
Make full file/db backup
Put up downtime message
Import TD into reputation system
There's a lot more. I'm looking at five hours straight. I'm literally nervous right now just thinking about doing it. You've never seen vB customized this much before.