USB device activity when not mounted

[Gary Aitken]

I can understand why I would see activity on a USB device when it's first plugged in.  But why do I see continued activity (i.e. the light blinks on a usb disk or memory stick)?  When I umount one of these, they keep being beat up on and it makes me nervous...  At what point is it sync'd and safe to unplug?  I assume when the umount returns, but what's going on after that?

Gary