To get it out of the way: Kindle rules. But, Amazon's flagship Kindle, now the Kindle Paperwhite, continues a trend that very much does not rule: forcing us all to use a touchscreen to navigate an ebook. That is wrong! It doesn't mean Kindle is a bad product--it still rules--but it could rule more, and we want it to rule more.
98% of your time with a Kindle is spent reading a book, rather than shopping or browsing or adjusting settings or whatever, which means the vast majority of your navigation is two commands: page-forward and page-back. The touchscreen is great for everything except for those two commands--it's much faster to select items in a list, for example, by tapping what you want rather than pressing the "down" arrow past all the things you don't want. It's also much easier to type in the on-screen keyboard. But having a touchscreen as the only option doesn't make sense: why would you opt for a control scheme that's great for the stuff you do rarely, and not great for the stuff you do all the time?
Here's why touchscreens are not great for ebook readers:
It's slower: This is a nitpick, but this entire article is a nitpick about a product I really think is great, so, you know, onwards! It is slower to operate a touchscreen than to press a button. That's one thing that's not thought about in the transition from paper to E Ink: turning a page takes much longer than pressing the "next page" button. Cool! Faster reading. But the touchscreen is also slower than a button. The old page-turn buttons are on the bezel around the screen, so your thumb falls naturally on them. You don't have to move your thumb laterally at all to turn a page; you just apply a tiny amount of force. But with a touchscreen, you have to move your thumb from the bezel to the screen, then either tap or execute and even longer page-turn gesture by swiping. Slower = worse.
Off-balance: Going along with the speed problem: moving your thumb means lessening the strength of your grip on the Kindle. On a bumpy subway ride, you don't want to be delicately balancing a $180 object on your fingers while your thumb gropes for the "next page" touch zone. You especially don't want to have to do that every minute, every single time you read a book.
Accidental press: After I transfer trains on my commute to work, touchscreen Kindle in hand, I sometimes look at the Kindle and realize I'm no longer on the same page I was when I stopped reading. Your hand brushes it, some drunk guy elbows it, whatever--that's a page turn. It's much easier to accidentally touch any part of the screen than to press a slim button on the bezel of a device. And there's no way to lock the screen to avoid that, because there's no other navigation at all: if you locked the screen, you couldn't do anything.
Tapping is hard: One of the great things about the Kindle is one-handed navigation, but it's much harder to do when you have to tap wholly different parts of the screen to navigate. If you hold the Kindle Paperwhite with your left hand, to go forward by swiping (nope! Blind gesture!) or by stretching your thumb into the middle of the screen, because tapping the left-hand side makes you go back a page. It's easier when holding the device in your right hand, unless you want to go back a page, in which case you have to stretch allllll the way over to the left-hand side. Awkward!
What grates is that the choice between touchscreen and buttons isn't a choice Amazon has to make. Usually I'm not in favor of having too many ways to do the same thing--it's my major beef with Android--but in this case I think it's essential. Barnes & Noble's flagship Nook, the Nook Simple Touch With Glowlight, keeps the page-turn buttons alongside the touchscreen. Buttons for turning pages, touchscreen for everything else. Perfect!
I don't want to suggest that the Kindle Paperwhite is a non-great product (we'll have a review up later this afternoon, and, um, spoiler, but it's great). The touchscreen problem should not stop you from buying a Kindle. This is a plea to Amazon: your cool thing could be a cooler thing. Make it cooler, please!