From my post on aiaio:
[The Apple] tablet’s pixels per inch will be impressively high, like the 160 ppi of the iPhone. Most Mac desktop and laptop displays hover around 110 ppi. An 11″ screen at 160 ppi will provide almost the same amount of pixel real estate as a 13.3″ MacBook screen does now. This will help minimize people’s perception that they’re giving up detail for size.
Apple wants an iPhone in your pocket, an iSlate (or whatever) on your coffee table, and an iMac on your desk, with laptops positioned for students and the mobile workforce. It’s ambitious. And more than a little smart.
If they can integrate the text book e-reader functionality of the tablet with iWork or Word on a MacBook every kid going to college will get one for high school graduation. Which makes the March drop date (and the 2 month announcement-to-holding-one anticipation period) very clever marketing.