There's this whole middle ground in personal devices that people can't get to work, and the problem is one of size. The PDA thing was useful when phones couldn't carry all of your information, but now they can. And so can your iPod. Viewing documents on a handheld device is useful, but the devices are too small for information entry. I remember sitting in meetings and watching people chicken scratch at their Palms and it just wasn't useful. That's what killed the PDA-- you can't use it to input information beyond to-dos, phone numbers and appointments and all of those things are better handled by your phone.
Once you make something big enough for document entry, it's too big to carry on a belt or in a pocket. If you need a bag for it, you may as well carry a laptop. There's room for smaller, lighter laptops, but they're increasingly niche products because they can't be full functioned. The smaller and lighter they get the more niche they become until you cross through the dead zone and get to phone size.
There's just no place for this, as far as I can tell.
