Didn't think about this before, and in retrospect, it's obvious, but it had me confused for a little while yesterday.
1. Put refracta on a usb stick with a second partition for full persistence (i.e. all files, not just /home).
2. Boot the stick in my computer. All is well.
3. Take the stick to a friend's house and boot his computer with it. No wired network.
4. Kill wicd, edit /etc/network/interfaces for eth0 to use dhcp.
5. ifup etho, and get error message saying that eth0 does not exist.
6. Look in /etc/udev/rules.d/70-persistent-net and see a big list of network adapters, the one on the currently running computer is at the end of the list. eth0 is back at my house on another machine. Look in /etc/resolv.conf and see my nameserver and domain listed.
7. Delete those two files (in #6), remove the entry for eth0 from inerfaces file and reboot. Wired network works automatically with wicd, as it normally does.