I'm going to have to break down and buy one. all the sport touring guys i know have them. They aren't any more of a distraction for most things than glancing at your speedo or tach. For a longer look you should pull over.
Lots of mounting systems out there. As said, depends on the GPS if you already have that. Otherwise you can buy a purpose built system.
I'm from the tank bag world too, and my GPS is folded paper stuffed in a map slot. I have to pull over to read it too.
I prefer a magnetic bag to do away with the harness. But i have a harness bag too and it's not much of a hassle.
Always a fear with the magnets what they might do to a camera, iPod etc. But I've never had a problem with either.