Absolute safest thing to do is backup the partition (or maybe only your files).
using dpkg --get-selections and a little scripting, you can get a list of every package on your system. pass that data into dpkg --set-selections and you get your old system back. So all you really need to save is home directories, /etc, and maybe /usr/local. Anything else is just not safe enough in my book. As for the physical move, /etc/fstab will need to be touched and lilo re-ran. Notthing else should depend on the name of the partition I can think of.
