I think one should bear in mind that iRex now have a sales partner in the US, so maybe shipping, returning et al aren't so hairy or expensive as before (
http://www.ereaderoutfitters.com).
For me, screen size was the clincher when I was deciding what to buy, but since then, seeing photos of the Sony Reader and the iLiad side by side have confirmed my choice for me, the resolution is not the same, those 16 scales of grey vs. 4 (my guess as to reason) make a real difference to image quality. And being able to annotate is nice, I got hooked on Sudokus.