Well.. I bit the bullet today and unbranded my Orange phone in order to carry out a firmware upgrade. The debranding was quick and easy although the guide identified on this site doesn't tell you to select "Virtual USB" when installing the NSS software.
The actual update from Nokia was straightforward but I was a little bit tense as 113MB of data was downloaded. Then during the update process itself which took as long as the download the screen of the phone worringly flickered a couple of times.
However, it's all done now and I'm glad i did it. I'd been having some GPS trouble and that's all cleared up now. I still need to get my contacts sorted again and reinstall a few things but everything looks promising.
Just one question... Is it worth reinstating the original product code or should i just leave it as it is...?