Flash thoughts - USB question
I have a 7Hi but the flash has never been an issue. I do tend to close it carefully though.
On the USB issue I have similar problems from time to time but normally with USB readers and USB key style devices. The message suggests that windows still thinks something has the drive mapped. This can be something like an anti-virus tool scanning the card even though you are not aware of it.
Other times I have sometimes left a folder window open somewhere on the desktop that is connected to the 7Hi or card reader so it still appears to windows as open.
Powering down the camera should be okay - so long as you are not actively updating the drive.