Everything went without a hitch, although when I restored my backed up files it didn't pick up clock settings, so when I used the device to blog the fact of my successful upgrade, it cheerfully created a post backdated to September. If I'd thought for half a second I would've realised that would happen. Anyway, everything's there and working.
I haven't tried out any Bluetooth functionality since applying the patch (it's late and I'm tired), but at least from the point of view of nothing terrible happening, I'm very pleased (well, relieved) with my first Pocket PC Phone upgrade experience.
PS. For any Harrier-owning Telecom NZ customers who haven't been able to find the patch yet (or maybe that was just me), the download page is here.