I actively cruised with my iPad. It turned out to be a true lifesaver. When I came into areas that I did not have a chip for it was able to let me know what exactly was below me at all times. At the time I only had the WiFi version but I was using the Sprint Overdrive which does have a GPS chip in it and the iPad was getting its numbers from there.
If you are planning on getting an iPad for Cruising, I recommend you get the 3g version. You do not have to pay for AT&Ts service to use all of the features you will need for iNavX or Navionics.
Throughout all of the storms my boat, me and my iPad survived the iPad never once faltered. I did take care to stow it when it was not in use and a if the weather turned bad. My iPad did take the occasional splash and spray but it never was submerged. While yes it is fragile, I do believe you will find it much more robust than you think.