Jon, the only real features that the Jetbook lacks that others might have are format supports and wifi.
I am not worried about wifi; I bought this to read books on, not to browse the internet. If I get a 2 GB card for it, I can probably download a few hundred books onto it and be happy for a year or two.
The format support concerned me somewhat, but once I figured out that it is fairly easy to convert .lit, .ereader and .mobi files into html and from there into .fb2, my concern was resolved. I hope they support other formats in the future, but I am confident I will be able to read whatever novel I want to on it.
Things I liked;
1. It simply acts as a USB drive on your computer; therefore unlike the Sony or the ebookwise 1150, no special hoops or software are needed to get books onto the device; especially since I have a Mac and a Linux box. I don't run Windows.
2. I like the fact that it is a bit smaller than than the 6" devices. I know the 6" devices are not huge, but for me the ideal device is one that will give me the most screen real estate possible that will fit in my pocket

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3. eInk is not really a mature technology yet. While it has a lot of advantages, its screen refresh time is not one of them. Also the glass substrate that is used makes it somewhat more fragile than LCDs (Granted in a metal design like the Sony, this problem is minimized). The grey scale LCD in the Jetbook is fast, and from the reviews easy to read and easy on the eyes. Now, I bet if we are having this conversation in a couple of years (or maybe even a year from now) this will not be true.. but I am not waiting a year to get an ebook reader.
3. It has no DRM based reader on it. Again, I would have been willing to go for eReader based DRM, but not any other scheme. So that being said, why should I subsidize Mobi or Amazon by buying devices that pay them to have their DRM format on them? I have no intention of using that DRM after all.
4. MSRP for the Jetbook might be $350, but street price is really $300, which is close to or considerably less than the street price of all the other major readers except the ebookwise.
Anyway, those are some of my reasons.
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Bill