Now that mounting /usr as a separate partition is fully supported again, thanks to the usrmove feature, I decided to try a new partition layout. This seemed like a good starting point for a small drive:
]$ df -h | grep sdb | sort
/dev/sdb3 497M 72M 400M 16% /boot
/dev/sdb5 10G 3.8G 5.7G 41% /usr
/dev/sdb6 5.0G 661M 4.1G 14% /
/dev/sdb7 22G 583M 21G 3% /home
I used to set up 10GB for root, and 5GB for var. It should be about right just making usr 10GB and root 5GB. Most of the root partition will end up being var after applications start populating /var.