My husband and I just got back from a wet, muddy dualsport trip through the Black Hills in South Dakota. I can't quite afford or justify a Nuvi, so I planned on using my phone as a GPS. I have a Samsung Galaxy S3, and I picked up one of these from RevZilla.
Phoneshield Samsung Galaxy S3 Mount Kit - RevZilla
I hooked up a handlebar RAM mount to my XT250, with the arm attachment, and a diamond mount for the case itself (
Amazon.com: RAM Mounts RAM-B-238 RAM 2.43" x 1.31" Diamond Base with 1" Ball: Car Electronics), since it comes with a smaller, cheap plastic ball mount setup. You don't *have* to use a RAM mount, but I'd recommend it for security, since the mount it comes with seems like it'll break with just the right amount of torque.
It comes with the ability to charge through the case, using a micro USB cable. Sometimes it works, sometimes it takes a bit of fiddling, cursing, physical motivation to get it to work... But the setup is waterproof and shockproof. It stood up quite well to the almost incessant rain on our trip, and didn't damage my phone one bit on the muddy and rocky ATV trails. Even after several drops on a particularly muddy section that required trailside removal of my front fender to get my bike unstuck.
I liked it enough that I bought a handlebar clamp RAM mount for my FZ6.
Amazon.com: Ram Mount Motorcycle Handlebar Clamp Base with M8 Screws: Automotive
However, another downside I found with this setup, is that the audio port doesn't really work well. I tried using it when my Ipod died, and couldn't get any sound through the earbuds. I might need a longer 3.5mm adapter to make it work, but I haven't tracked down the one I already have to test it out.
Also, unless you shade the screen with your hand on a sunny day, the glare makes it tough to make out the maps. But it will work with most thinner or smartphone-friendly gloves.