I'd like to repartition my disks, move some dirs off to their own filesystems. Any ideas on how I might do it?

Oh, just noticed that I can shrink existing partitions. That'll make it possible.

Using the LPM, if you've already partitioned all available space, you can resize your current partition smaller (if you have the free space), then create your new images, boot back up, mount them, copy your files over, edit your configuration to assign drives, edit /etc/fstab to mount where needed, reboot and you should be good to go. Just be careful not to mess up your fstab settings to where it won't boot, otherwise you'll have to additionally do what Ciaran suggests in this thread:

http://www.linode.com/forums/viewtopic.php?t=1416

Edit: Just noticed your second post while I was double checking that I wasn't missing any steps.