Yep, sometimes I think the people complaining about eyestrain are still thinking about 60Hz CRTs. I think I'd slightly prefer e-ink for lots of reading (though a backlight is important to me), but I never have any feeling of pain or strain while reading on my iPad. (Perhaps others' experience is different, of course.) If anything, I just want it to be sharper like a high-res phone display.
One of my co-workers told me that he prefers reading ebooks on his iPhone 4 to his iPad - we side-by-side compared them, and the iPhone screen density makes a huge difference.
That said, the form-factor is a little awkward for longform reading.
This is a key point: the iPad's display is only going to get better over time, while e-Ink displays are probably not going to improve much from here. They might get faster, but what else is likely to change? I can't imagine investing in a company that spends time optimizing an e-Ink display. It would be like building a better vacuum tube.
When the iPad gets the so-called 'retina display' from the iPhone 4 model, it's all over.
