Something tells me that the people posting on this thread with the position that a regular LCD screen is fine for reading books and that e-ink is bs aren't people who own and use e-reader devices with e-ink displays.
Before I got my Kindle2 I used the Kindle reader app on my iphone. I used it to read a total of 5 books. I found the display to be fatiguing to look at for a long time. When I finally got the Kindle, I felt much more like I was reading print on actual paper. The viewing angle is only limited by being able to see the screen and in a brightly lit environment, the display only gets better. On a sunny day I find the displays on both my iPhone and my MBP to be very hard to see because the ambient light is brighter than the backlight of the panel. Also, the display of the Kindle is matte, so there's less of a problem with glare.
Another plus of the Kindle (and the Sony for that matter) is the size and low weight. I'm probably in the vast minority of Macrumors members in that I ride a commuter train and then a subway every day going to and from work. Most times on the subway leg, I have to stand. I first tried the Kindle DX and I found the larger size and the greater weight to be uncomfortable (and problematic in terms of personal space on a crowded train) and I returned the DX and got the regular Kindle after a couple of days. I don't see my self standing on a crowded train reading a 1lb 10" device with the viewing angle of a regular LCD screen. As for the low number of ereaders out there, well again, maybe my situation is unique, but I see more and more of my fellow commuters with these devices, especially Kindles. It's rare these days that there isn't someone within visual range using one.
So, are people going to read books on the iPad? Definitely. Will they enjoy it? Probably. Would I put down my Kindle and instead read books on the iPad? Definitely not. That said, I'm still planning on getting an iPad because I think it'll be a good device to have around the house for more comfortable browsing than the iPhone. When I get it I don't plan on taking it out in the wild.
John