iOS 4.2.1 GM. UUID??

In my admittedly limited experience, GMs do not require it. I do not have one.

I don't have one and installed the latest GM (from restore mode) with no problems.

Nope. I don't have one. It can be installed either as a Restore or as an Upgrade without a problem.

GMs do not require your UUID to be registered and I found even with older versions I forget to register my UUID on my iPad (Wi-Fi) and it installed with no issues. It seems only 3G iPads need to register your UUID on a developer account.