I upgraded yesterday. I didn’t want to lose the settings data in my apps, such as saved login info; and I didn’t want to re-define my list of synced music. So I after the upgrade, I restored my user data from my last backup.
This is too bad because I was hoping the restore would restore my apparently corrupted carrier name string. Some Cydia app named MIM that SH referred me to blanked it out but won’t restore it to the default. [Update: This was actually a bug that was eventually fixed in a Dev-Team jailbreak or unlock, I forget which, not MIM’s fault.] And I think that creeped into some other storage/settings area the other day and caused me to not be able to send calls and text messages until I’d rebooted and mucked around with a bunch of settings. Phone was restored on reboot, IIRC, but SMS too more fiddling. What a pain in the rear.
The upgrade to OS 3.1.2 from OS 3.1 went fine. I used Pwnage to make the custom IPSW, as I did when I upgraded to 3.1.