I'm using Transas iSailor successfully.
I'm also using Garmin Bluechart successfully, now that I've discovered that there's a limit to how many chart sections can be downloaded onto the iPad at once. When I downloaded all of Hawai'i, southern Alaska and British Columbia, Bluechart would quit without warning, but with a smaller area of coverage it's stable. It carries more information than iSailor, with Active Captain and tides and weather being available if there is an internet connection.
If there's any question of the iPad being exposed to moisture, I put it in a Ziploc bag, and the touch screen still works. A more robust solution would be a clear plastic map case, as used by hikers. I don't mount the iPad, but keep it on the chart table (next to the paper chart, Kurt), and when I'm doing anything where I need up to date position info (entering a port for the first time at night, for example), I put it on the companionway step where I can see it. However, if you do want to mount it, there are now a huge number of iPad mounts, particularly:
"Tested and certified to meet or exceed US Department of Defense Standard 810F, Griffin's Survivor Military-Duty Case is designed from the inside out to protect your iPad from extreme conditions ... dirt, sand, rain, shock, vibration and a host of other environmental factors."
The iPad does make a good chart plotter. It has a good daylight viewing screen, it is easy to zoom in and out, power consumption is low. It is much to be preferred over a laptop, for real-life, on-board navigation. It is not 100% reliable, and neither is a laptop - you have to go to a very expensive big ship system before you get ECDIS, a computer-based navigation system that complies with IMO regulations and can be used as an alternative to paper navigation charts. Keep some form of paper chart and separate GPS as backup, but then enjoy navigating your boat confidently between hidden dangers, knowing where you are in real time on the chart. More information is always better than less. The iPad adds another layer of information to the traditional paper chart, GPS, plotting tool, pencil and eraser, but doesn't totally replace them.