As Bill has said,
http://www.marinetraffic.com is a good site. May not work in the middle of the Atlantic but as the ship approaches the English Channel it gets much more accurate. I was logging on regularly when mine was sailing up the Channel and in and out of Gothenburg (wife rolling eyes whenever she caught me on the website!). There are also webcams at some of the ports if you're super keen but I couldn't see much. Some more info for the fanatics here
http://www.bmwblog.com/2009/07/14/ho...d-to-delivery/