A professed sailing newbie with his first boat about to go in the water in a week asks how many use their cellphones for GPS navigation. I have the Samsung S3 and the lite version of "marine navigator". Having tested it while on other boats it appears to track things very well. I downloaded a bunch of appropriate NOAA charts and cold see everything I needed to see to get where I wanted to go. So is this something that is catching on in the sailing community or are we still advised to purchase stand alone GPS/plotter equipment. I am sure the phone software has limitations but it is tough to beat FREE. Plus the professional version is only like $6.
I had the lite version and bought the paid version. It's very nice - definitely worth the money. I didn't really need it but wanted to pay the guy because he did such a nice job with the app. However, I found it very useful for use on the dinghy when I chartered in the BVI a few months ago. I'd mark my spot when we went out for dinner, and could use the cell phone to find my way back to the boat after dark. With dozens of boats in most anchorages, it was very useful, especially since I had my cell phone with me anyway.
The main complaints I hear about apps like this for phones and computers is from people who can't figure out where to get the charts and how to load them, or they just don't want that hassle. Sound like you've already solved that problem, and as you've noticed, it's a only one-time hassle.
As for paper vs. electronic, that's almost a religious debate. I have a handheld Garmin GPS that has been very useful, but I see no reason why a good smartphone won't completely replace handhelds very soon, just like they're replacing automotive GPSs.
I would suggest you get a waterproof case for your phone. Search "DryPak" on ebay.