Hi Simon,
The feedback that I promised: It makes no difference whether the Desire is locked or unlocked at the time of PC shutdown or boot and it also makes no difference whether it is in "charge only" or "mounted drive" mode when shutdown is inititated; the PC's subsequent boot "hangs" immediately after performing the memory check.
I additionally now know however that if the USB lead is pulled out of the Desire whilst the PC is hung, it immediately (absolutely no discernable pause) resumes booting all the way to success; handy to know that I don't need to go through the BIOS battery palava given that I probably will sometimes boot the PC with the Desire attached.
XV