I bought my iLiad used at half-price right after the Sony Reader came out, from someone who wanted to switch. It has worked out very well for me, but I do understand the complaints about boot time and battery life. I like the open development environment, though, I actually prefer the screen size, and the stylus input is critical as I bought it in part to read and annotate journal articles for my graduate studies, and to take notes in class.
And to read books, of course.
If Sony's next version has some kind of wireless/cell connectivity AND they do a deal with Borders Online, they might catch up with the Kindle. Otherwise, I think anyone with similar features and a lower price point is going to eat their lunch. I'm quite curious to see how well Astak does (if they ever get their products out the door).