In Massachusetts It is illegal to have video being displayed on any screen visible to the driver unless the parking break is engaged. If you had a Windows desktop with netstumbler and winamp going they MIGHT be able to bust you. Chances are you could just contest the ticket and the cop would never show up or you would win.
Recently in Boston however there was a guy who was pulled over and ticketed 3 times for having an air freshener hanging from his rearview mirror. They called it obstruction. Because I have no modding skills I had to use the stock mount that came with the unit. This makes it a bit higher then I would like and blocks my vision of about 6 feet in front of my car on the far right side. Technically itís obstructing my view (Not that I ever look where it obscures).
Navigational software is perfectly legal to have on a screen visible to the driver.
My solution is to just keep copilot up. I don't really need to be poking at anything else when I'm driving as I control winamp through a powermate and I have a nifty OSD plug-in that tells me the song name. If I get pulled over It's just a navigational program. Because of the fiasco with the air freshener guy and the bad press it earned the MA police, they won't bust me for obstructed vision.
Iíve driven past cops in my town quite frequently and never had any problem. Itís just something to be aware of.