Not sure what I'll do with my 3GS since it runs just fine on the 4.3.3 jailbreak. I'll be getting a new phone either way once the next iPhone is released (iPhone or otherwise).
I've really been looking foward to ios 5, so I will probably end up getting it asap. It really depends on how soon the next iphone come out as well. If it comes out pretty soon I may just wait, so I can sell my 4 jailbroken.
Definitely first day. The iPad being simpler than the computer, unless they really fowl things up, I don't foresee any real problems with the upgrade. The new features are way too tasty to pass up, even more a day.
As soon as I get home from work on release day, I will be updating my iPad and iPhone 4. Hopefully updating later in the day will avoid a mad dash of users who will update first thing when Apple makes the software available for d/l.
When there is an untethered Jailbreak (UJB) ... it doesn't matter if Apple updates to 5.0.1 or 5.0.2 before the UJB because then they can't patch the exploit ...