If you care about electricity usage, then it might pay to assemble your own Linux-based firewall / DHCP / NAT / NAS / PrintServer / email-server / WebServer / whatever box. Suprisiingly easy to do these days. Mine is a mini-ITX mobo, with a laptop 80GB hard disk (courtesy of Paul). Draws 18W at typical load, measured at the AC power cord plug.

Cheers