Windows: Asus' Ai Charger is a free utility that lets you charge the iPad from your PC's USB port, which otherwise doesn't offer enough juice to charge the tablet. Ai Charger also promises to charge iPhones and iPods 50 per cent faster using standard USB ports.
Blogger Matthew Hunt posted this chart comparing charging time for the iPhone 5 with Ai Charger versus USB 2.0, USB 3.0 and the wall charger. In this test, Ai Charger is about as fast as the wall charger!
Ai Charger apparently works by sending up to 1.2A through the USB port, so charging your iPad via USB won't be quite as fast as through a wall charger. Still, this means you can travel with your laptop and iPad and leave behind the power brick if you want to.
Asus says the Ai Charger works with all motherboards and systems, but because it's hacking the power going through the USB port, this is a use-at-your-own-risk utility, and your mileage may vary. After installing Ai Charger on my Dell laptop, my iPad went from "Not Charging" to charging up. Some folks over on XDA Developers are even reporting the utility works on some non-Apple devices.