It's really cheesing me off that I can't ever umount my removeable drives without killing X first because Gnome's act of displaying them makes the system think that the device is busy.

Mount a device and get to the point you would unmount it.

In a console type
lsof | grep /path/to/mount/point
to see what is actually using it. My guess is it's famd or something.

daniel@aopen25:~$ umount /dev/sda1
umount: /media/usb: device is busy
umount: /media/usb: device is busy
daniel@aopen25:~$ lsof | grep /media/usb/
lsof: WARNING: can't stat() ext3 file system /dev/.static/dev
Output information may be incomplete.
daniel@aopen25:~$ umount /dev/hde1
umount: /mnt/hde: device is busy
umount: /mnt/hde: device is busy
daniel@aopen25:~$ lsof | grep /mnt/hde
lsof: WARNING: can't stat() ext3 file system /dev/.static/dev
Output information may be incomplete.
daniel@aopen25:~$

FAT32 formatting has many downfalls, but it's the price you pay for being able to use it on other people's computers.

EDIT:
Ok, mixup on my part, suid is enabled on Nautilus but i just has nosuid on my /usr directory, must have put it there by accident when I was adding it to other drives. Even with that problem fixed, I can still only umount a drive using the graphical command, not the command line. Suppose that's liveable.