Barnes & Noble's new touch-screen version of the Nook, introduced today is both a counter-attack on Apple's iPad and a way to gain an edge on Amazon's Kindle. I like my iPad as a device for watching videos and surfing the web, but it's a bit unwieldy as an e-reader. (I have the original iPad, not the newer, lighter model.) This weekend, while using my sister-in-law's Kindle, I was reminded how light and purse-friendly it is (though I had a strange urge to flip it like a Frisbee). The new monochrome Nook, which sells for $139, is also feather-light -- it weighs 7.5 ounces and is less than a half-inch thick.