I am doing more and more reading on my iPhone these days. Here's my quick ratings of usability of several techniques deployed in widely used applications.
My eyes get tired and when the do, I need reading glasses for small fonts. I am therefore looking for a reading control in which I can adjust the fonts to a large enough size to read text quickly and easily. The 3GS I use has a screen resolution that is great for its crisp text even at small font size - as long as I can focus my eyes on it without tiring them. The 4G's retina display makes text even crisper, but this doesn't help if one has trouble focusing.
Safari and apps that simply open a web page view: Grade B-. You always have to zoom in, and in general you have to pan the screen a lot to see the left and right parts of the text. Not pleasant, but far, far better than the 'old days' before full-powered web browsers were available.
iBooks: Grade B+. You can make the font look like you want, and flipping pages is relatively easy. But you still have to flip those pages, which can be irritating as your finger has to move a lot, and it gets in the way of the text a little.
The Globe and Mail app (powered by Spreed): Basic text mode reading: Grade B+. Much nicer than reading the Globe and Mail in Safari. You can't use gestures to increase font size, but default sizes are quite readable. You flick to scroll down like a web browser. Spreed mode: Grade C. This is highly touted as a way to read faster. Groups of grammatically-related words are flashed in front of you at the speed you wish to have them appear (from 260 to 1000 wpm). The instructions say that you will get faster at reading with time, and that you should not care about the odd word you miss. The trouble is that in my experience the odd word is critical. I read one article, missing a key 'not' because I didn't have time to 'take it in' before it disappeared. I therefore ended up understanding the opposite from what the article actually said.
Instapaper's tilt scrolling: Grade A. This wins hands down. I look forward to the day when all mobile devices use it natively. As you start reading each article, you press a little icon at the bottom and then tilt the screen back a tiny bit to make the text scroll slowly. The slightest movement of your hand can speed up or slow down the scrolling, meaning that the text you are reading can always be kept in the centre of the screen. I can still suggest some improvements: As an option, it would be nice to be able to start the scrolling with a very small gesture (a shake or a large tilt). And perhaps other kinds of gestures could be used to navigate from article to article, including archiving the ones you have read. I think it would also be nice to have greater control of how the amount of tilt maps to the amount of scrolling speed, just like in 'mouse speed' preference panels found in operating systems.
I am not the first to praise this technique: See also http://thehomescreen.blogspot.com/2009/04/tilt-scrolling-for-win.html.
Maybe if tilt scrolling became the norm, Jakob Nielsen may consider updating his ratings of reading speeds for touch screen devices.