Will, there is an other interesting source here:
under the flash-animation there is a download link for the shapefiles,
This looks like a very nice dataset, a shapefile for every month and very detailed too. But there is one catch: it's showing the coastlines of the 1990s/2000s, and several bodies of water are omitted, in the case of The Netherlands this is wrong. It's not really a big issue at the scale Will is going to be working on, but I wanted to point it out anyway, in case somebody else was going to use the data as well.
[sorry... pet peeve of mine]