Mine runs tor, squid, dansguardian, samba, NFS, sshd (naturally), transparent proxy (iptables rule so the kids cannot by pass the proxy, 6in4 tunnel (sixxs), dns, dhcp, some other stuff I've forgotten about
Added an eSATA 1TB disk and it flies. Also has a 100GB usb disk as a backup for my photos - rsync's them once a week. 4 watts + whatever the external drives use. Tons of ram and cpu left over...