I have a jailbroken NZ iPhone 3G still running 3.0 firmware.  Looking to upgrade to 3.1.2 and re-jailbreak.  I only have access to PCs so Blackra1n would be my only jailbreak option.  I have read of a few people having issues with tethering and wifi connectivity after jailbreaking with Blackra1n, is this still a problem?

Once I update  the firmware to 3.1.2 it will change the baseband version and apparently you cannot revert after this change is made.  This prevents unlock hacks from working, but I don't think it will be an issue as NZ iPhones are sold unlocked anyway.

Also, what options are available for backing up jailbroken apps I have downloaded? Is there an easy way to keep all files and settings in tact, upgrade to 3.1.2 and then re-jailbreak using Blackra1n?  I believe all my stuff gets wiped when upgrading the firmware.  Could I back up the iPhone and then restore it once I am at 3.1.2 firmware and then jailbreak.

Can anyone share their experiences with this?