I've been thinking a lot about this, and with the upcoming release of the Asus eepc t91 I think we might be getting closer to a netbook that will serve as a good ebook reader.
The Assus T91 is a fully fledged Netbook with an 8.9" screeen, 16GB SSD, webcam, SD slot all the usual suspects. But the t91 has two features that would make it a good ebook reader for a lot of people. Touchscreen and tablet format. You can swivel the screen around into a very comfortable looking and touch driven screen. Perfect for those pesky PDF's and colour comics, along with anything else that can be read on your computer. Also they're claiming 5 hours battery.
The asking price for this is rumoured to be in the £450 mark, but remember this is a fully fledged computer, not just an ereader. Here's some video:
So what do you think about the t91? Will the dedicated e-reader become a tiny insignifcant niche in the face of cheap and powerful netbooks? If they do become more popular, will we see the adoption of PDF across the board as the 'ebook' standard?