Just a quick tip. Bringing it up because I couldn't find a good solution from googling around.
After following one of the many posts on persistent usb installs, I would lose my changes to /etc/network/interfaces on reboot (it would revert to the default contents).
Based on some brief poking at initrd.gz (scripts/casper-bottom/23networking), it seems you can fix this behaviour by adding "STATICIP=frommedia" to grub's menu.lst. So the relevant entry on my USB stick now looks like:
Not sure if there's a better way to do this, but it seems to be working.
title Start Persistent Live CD
kernel /boot/vmlinuz BOOT=casper boot=casper persistent rw quiet vga=0x317 STATICIP=frommedia