Well I tried reinstalling the ROM image, but ActiveSync still refused to restore the data because it was made by a "different device". I am using ActiveSync as GUEST by the way, since the update removed all the Partnership info.
Someone else suggested that I try changing the ower info and making sure all my settings were the same etc, and perhaps that will trick ActiveSync into behaving.
Otherwise I guess I'll just have to bite the bullet and reinstall everything *groans*

Oh well, you live and learn.
By the way, when you talk about PIM data, do you just mean all the stuff that's in Outlook, or is there a way to recover all my settings etc without restoring from ActiveSync?