The biggest open question regarding the iPad's potential as an e-reader relates to its bright, LED-backlit display. Amazon's Kindle uses E Ink, which--while much duller and darker than an LED screen--is decidedly easy on the eyes. I can read my Kindle for hours, with no eyestrain afterwards. But before I bought the Kindle, I tested myself (to see if I would actually stick with an e-reader) using the . And while I did read several full books on the iPhone, the eye impact was definitely noticeable; I needed frequent breaks from the brightness to rest my eyes.

Eventually, the Kindle app added a "nighttime" mode, where the app offered white text on a black background. That made reading, particularly at night, far less bothersome, and I could go for far longer stretches. But again, once I started reading on a genuine hardware Kindle, the eyestrain was no different from reading an actual book (remember those?).

For the iPad to compete, then, Apple needs to figure out a way to keep things as easy on the eyes as possible, while using that LED screen. The iBooks demo revealed that Apple's reader app shows the text as a virtual book--you can see the pages "behind" the one you're on in portrait mode, and landscape mode actually shows facing pages of the book realistically. Will iBooks offer a white-on-black mode? I don't know how weird it would look to show a photo-realistic book with black pages, but an approach like that seems necessary for extended reading times.

A second big question for me is how the iPad will handle bed-based reading. Using the iPhone while lying down can be a small exercise in madness; the screen often wants to flip to landscape mode, even though you're holding the iPhone vertically. (That's because the accelerometer can't work its magic quite as well when you're in that position.) The Kindle app eventually addressed this shortcoming with an orientation-locking mode. Frankly, I think the iPad will need such a feature system-wide (you won't want other apps flipping on you either), but it's an absolute must for iBooks.

A third feature of the Kindle that I didn't initially see the need for, but I've now grown quite fond of, is the integrated dictionary. You can move the cursor (painfully slowly, given the Kindle's lack of a touchscreen) to the word in question, and a definition appears along the bottom edge of the screen, without obscuring any of the book's text. If I could double-tap a word on the iPad to get an easily-dismissible definition popover, I'd be delighted. Apple hasn't demoed such a feature thus far, but let's keep hoping.