Cool... with the D300 you can go a couple different directions. Initially, I bought a Nikon cable (it's an MC-35) that I could use to directly connect my Garmin to the D300. That worked very well, although I found the combination to be a bit bulky. It's ok, but there's a lot of cable and it's kinda awkward.
A few months ago I found the "Macsense Geomet'r" receiver, which plugs directly into the D300, and can be mounted right onto the hotshoe. It connects through the 10-pin adapter (like the MC-35 cord does). I velcro my Geomet'r to the camera strap, and it's not cumbersome at all. I like this combination a lot, and use it for vacations, etc.
As an example, I posted a bunch of our Christmas cruise photos on Picasa, which can automatically create maps based on the EXIF data: http://picasaweb.google.com/alansfreed/ChristmasCruise#
I looked through your pictures and had to chuckle. I'm from Pittsburgh and am sailing on the Independence too. Was on Freedom a couple of years ago, but am still a fan of Serenade. The wife and kids like the mega ships better so all's good. I would really like to get the Macsense Geomet'r but will wait a few months before I try to sneak the buy past the wife. Did you have any problem with condensation forming on your lenses? I had a 20D that was very problematic in the Caribbean, condensation would form on the backside of the lens. I know the D300 is supposed to be weather sealed so I'm hoping internal condensation will be minimized. Also, what lenses do you use? I just dumped Canon and moved to Nikon so I'm rather new to the Nikon scene.
Thanks for the information!