When I saw the car. After all,
Then I thought it over more carefully and realized that using the iPad in the car is probably a horrible idea.
It's probably not a very good GPS device
That low, low price of $499 gets you an iPad with built-in Wi-Fi, which can guess your position with limited accuracy using the location of a paired Wi-Fi hot spot. However, it will be plagued with the same issues that keep the iPod Touch from being useful for navigation. It won't be able to track your position when you lose your Internet connection--such as on an interstate. To make matters worse, the built in Maps application won't be able to access map data once its connection to the cloud is severed.
While the map data issue can be solved by downloading an app that stores maps locally, to get the always-on 3G connection and the real A-GPS tracking that comes with it, you'll need to step up to one of the iPad 3G units and pay for a monthly data plan. A standalone GPS device or that smartphone in your pocket is much cheaper at this point.
It doesn't multitask
While we're certain that the iPad will be able to access your iTunes library from within a navigation app and run the Mail app in the background (not that you want to be checking mail at 70 mph), that's about the extent of its multitasking capabilities. Anyone wanting to navigate while streaming audio from Pandora or Slacker using their fancy-pants 3G connections will be out of luck.
It doesn't make calls
For as low as $199, you can buy a portable navigation device with multimedia capabilities and a built-in cellular connection for voice and data. It's called the iPhone 3GS. For about the same price, you can get a standalone GPS device that will act as a speakerphone via Bluetooth. At $629, you can get an iPad that has a data connection, but you'll be out of luck if you try to make a call from it or through it. This is definitely a case of less is more.
It's too damn big
Seriously, where did you think you were going to put a 10-inch screen in your car? Mounting it on your windshield or at the top of the dashboard will obstruct a good deal of visibility and all but guarantee that you'll find yourself on the receiving end of a ticket. Mounting the iPad lower in the cabin will mean that you'll have to take your eyes off of the road to view the screen and, if you're using an iPad 3G, will most likely result in compromised access to the sky, limiting GPS accuracy.
It's not very modifiable.
One of the reasons that the Mac Mini makes such a cool carputer is that it is fairly easily modified with third-party software, peripherals for GPS, Bluetooth, additional storage, and custom interfaces optimized for in-car usage. The sky is the limit when it comes to a computer; however, the iPad isn't really a computer, it's a device.
You're pretty much stuck with Apple-approved applications and peripherals. Even then, the multitasking lockout prevents many of these additions from really being useful. Sure, you could get around such restrictions with a jailbreak, but that's a scary and dangerous route when you consider the possibility of making your iPad into a $500 brick.
Most importantly, it's too much of a distraction
Where I come, from we have a saying: "Sense ain't always common." Though we'd all like to believe that drivers are smart enough to keep their eyes on the road, trust me when I say that they're not. We live in a world where you have to pass a law to get people to watch the road and not their phones.
So, if you think those who text while driving are a menace, wait until you find yourself trading paint with people who are trying to read the Times in traffic, play Sudoku while waiting at a red light, or watch a video podcast at cruising speeds.