FYI, the nice support folks at zoneedit just solved an occiasional but 
recurring problem with dynamic dns, where the dynamic update did not 
always occur.

The solution is to provide an entry for the Server paramter ("which can 
usually be left blank"). They suggest using dynamic.zoneedit.com. Thus 
the config for Zoneedit becomes:

Service Type: ZoneEdit
Hostname: the host you're trying to update (i.e. the dynamic name)
Server: dynamic.zoneedit.com
... the rest are default values ...
Username: <your zoneedit account name>
password: <your zoneedit password>

Hope this helps someone!

cheers, michael