At the moment, IMO, they are too fragile so their size is inconvenient by the time you have allowed for a safe storage cover. If the screens became stronger, then they would be closer to the size of a book and they'd start to make more sense.
Although, I rather like books.
I'd prefer to see them becoming more friendly as news readers, with content regularly updated when in reach of wireless networks. At the moment, I do a lot of news browsing on my phone, it would be a lot easier, quicker and more legible to have the news delivered to an e-reader which could also store content to be read when out of the reach of mobile signals, for instance, when underground. You could use it to keep, for instance, a month's worth of copy from a magazine or newspaper to carry around. Although the hardware is too expensive at the moment, if the readers themselves were more affordable, I'd pay a subscription to get content delivered to an e-reader.