The guy sitting in front of me at the Swiss @-print conference today spent some time browsing through articles on his iPhone when the speaker’s topic didn’t interest him.
That’s a cropped version of a zoomed image I took with my 3GS camera, and it’s rather grainy. I don’t know if you can see just how small the text was on his screen, but it was pretty small. From what I could see, I’d guess he had about a third of an A4 page displayed horizontally on the iPhone screen. In that case, the text would have been about 60% of its printed size at best, and most scientific journals aren’t known for their large easy-to-read type.
Since I got my first iPhone, my nearsightedness, which had stabilized over the past years, seems to be getting worse again. I even had to get reading glasses. I know a few other people who have complained of the same thing since they’ve gotten an iPhone, too. It would be interesting to know if we’re part of a larger trend.
The well-prepared mind 
Fondled the iPhone 4s today. Hadn’t touched an iPhone 4 for months and months. Was shocked at how damn teeny the thing was, especially after fondling an iPad. I was surprised people could even hold the iPhone 4s without it slipping from their hands. He probably didn’t want to pinch zoom or was stuck reading something that couldn’t reflow.
Yes, I think it was a pdf. The best you can do with those is landscape zoom to fit the width of the text on the page. Even so it’s only really useful for emergency reading.