Partitions on a USB Drive

I'm just experimenting right now to find a type id which both Windows XP and Ubuntu 9.10 don't support.

Well, the list can be found, here

http//www.win.tue.nl/~aeb/partitions/partition_types-1.html

But I guess that I am missing something. Changing the TYPEID may make it impossible for the OS to mount the partition, but it is a simple process to change it back in order to make the partition visible, again, so what would be the point?