I have a similiar set up to Matthew's, butI use Delorme's TOPO USA software. The set of cables I use also provide power to the gps, and I have an inverter to power the laptop, so GPS and Laptop batteries are of little concern. Works really well, but it the laptop and cables do clutter things up a bit. I mainly use this if I'm offroading in unfamiliar areas.....
My ultimate plan it to mount a laptop docking station under my seat, that inturn would be mounted on a breadboard type of pull out drawer for easy access. That would remove the laptop off my seat, and everything else as follow, could be permanently mounted....
I would also use a foldable keyboard that I could tuck away when not in use, use a wireless air mouse such as those made by Gyration, so I don't need a mouse pad. And lastly, I would utilize a removable 9" monitor that I could mount on my dash. All this of course hardwired into place.
The docking statiion set up allows me to keep the mouse, foldable keyboard, and monitor permanently mounted....and I'd still have a great GPS system but without the clutter. With this set up I could also pull up to Wifi hotspots and websurf from my XJ.... how nerdy is that? :roll: