I finally decided to tempt fate and do the upgrade from 3.0 to 3.1 and set out to use pwnage to make the custom ispw on my wife's MacBook and then use this file to do the restore on my own Windows machine. However each time I tried I got the well known 1601 error. The iPhone was in DFU mode OK but it just wouldn't work. Some of the solutions I read suggested various combinations of closing iTunes, unplugging and plugging the USB cable, but they all seemed to be a bit flaky so I ended up using the MacBook with the same ispw file and everything went like a charm. So perhaps there is something that doesn't agree with Windows when using pwnage to create the customn ispw file.
But on a brighter note, before doing the upgrade, I also used AptBackup to do a back up of the non Apple apps on my phone. Once I had synced my phone to reinstall all my Apple apps and other settings, I downloaded AptBackup, ran the restore function and every single one of my Cydia apps was reinstalled painlessly. The only thing I had to do manually was install the Appulous Mobile Substrate patch to enable ipa files to be installed. And Ultrasn0w worked perfectly to preserve the unlock. The only issue is the lack of carrier logo, but this is hardly vital.
So it looks as though it's best to try and use a Mac to do the upgrade; but AptBackup makes it all very painless.
But on a brighter note, before doing the upgrade, I also used AptBackup to do a back up of the non Apple apps on my phone. Once I had synced my phone to reinstall all my Apple apps and other settings, I downloaded AptBackup, ran the restore function and every single one of my Cydia apps was reinstalled painlessly. The only thing I had to do manually was install the Appulous Mobile Substrate patch to enable ipa files to be installed. And Ultrasn0w worked perfectly to preserve the unlock. The only issue is the lack of carrier logo, but this is hardly vital.
So it looks as though it's best to try and use a Mac to do the upgrade; but AptBackup makes it all very painless.