I too could use this functionality in m0n0wall. It seems kinda lame to have to run the ip updated on a lan machine that may or may not be on all the time as opposed to my m0o0wall that is *always* on. Current uptime is only 53 days... would be longer if I hadn't tripped that breaker
Seriously though... Im not saying I have the skill to do this myself... but... it cant be very difficult to implement the ip updater client.