I am using topo maps, with the Charles wells/fun treks books which come with free corresponding GPX files. I have the top of the line iPad 2 with gps. I will say I prefer overland navigator which I have on my laptop and used to have mounted with a tray style ram mount but the hard drive was getting punished. With the survivor case and the solid state HD in the iPad it is way friendlier.
To answer the visibility question I am only missing a small corner of my passenger side. With the 360 ball the x mount sits on I can lower it to sit in front of my stereo but it would need some additional support to the dash for stability. I am working on that as a solution/alternative. Where it sits now was really not that bad.