The concept is similar to what I plan on doing to my 2000 ES, however, I won't be paying $2,000 for a Q-PC that isn't even integrated into the car so as to look stock.
If you know a little about computers you can take a look at the motherboard
I'm planning on using in my custom built solution. As you can see, it's quite small and can easily be retrofitted into a on or two DIN-sized case (depending on what I throw in there) for easy installation into a car. The plan is to have the LCD screen (6.4" or 8.4" depending on what I can fit in the dash after moving the digital climate controls to the space the 4x CD changer occupies) have a touchscreen interface in order to better facilitate user interaction while driving. I will also be making a little custom launcher application that will place large buttons on the screen that, when pressed, launch an MP3 player, GPS app, etc. If I can work out a decent system of interrupting the MP3 player (perhaps a push button) and accepting voice commands I will add that as a method of UI.
I will not be installing a keyboard as it looks clunky. I will (potentially...dunno yet) be placing push buttons around the display that will emulate keystrokes in order to accommodate input that isn't possible with a mouse. I've also toyed with the idea of putting a keyboard/trackball combo into the fold-down armrest/cup-holder in the back seat for those that really want to use a keyboard.
I figure by using an extra battery as opposed to the main battery in the car I can keep the power somewhat clean and also prevent drain on the main battery. I just have to figure out a way to make the secondary battery charge off the main while keeping it isolated from the power drain of the car. I do computers, networks, etc....not car mechanics.
Anyhow, I'm still in the prototyping phase and don't have any pictures as of yet, but I think you can get the idea.