This is according to Mediafour (makers of MacDrive): How To...Safely remove drives from the computer
Even though FireWire and USB devices
are Plug & Play (i.e. they are ready
to use upon being plugged-in), you
should not just unplug them. By
unplugging a drive with a "hot"
connection, you can corrupt data on
your hard disk or other storage
device. It is important to note that
even disconnecting a device improperly
one time can cause file system
corruption.
You can prevent such problems by
clicking the "Unplug/Eject" or "Safely
Remove Hardware" icon in the system
tray (down by the clock). The icon
looks like a gray box with with a
green arrow on top.
You'll then be given a list of
removable devices that are currently
connected to your computer. Highlight
the device you would like to remove
and click "Stop".
Windows should then prompt you that it
is safe to disconnect the device. If
not, this is an indication that some
part of Windows is using resources on
the disk. To clear this, reboot your
computer and before doing anything
else, try the above instructions
again.