Mary Tripsas, a professor of business administration at Harvard University, who studies the e-reader industry, says that companies are still trying to figure out the best interfaces for e-readers. "I don't think anyone's gotten it right yet," she says, although she adds that it is a good idea to make it easy to keep track of annotations to documents.

At this stage, the interface may not be enough to distinguish one e-reader product from another, says Susan Kevorkian, an analyst at research firm IDC. "The primary factors for the e-book reader market have been content availability and device price," she says. Plastic Logic has so far announced publishing partnerships with several Detroit newspapers, the Financial Times, USA Today, and content aggregators such as Ingram Digital, LibreDigital, and Zinio. The price has not been finalized, but Glass says that it will be close to that of other e-readers on the market.

Ultimately, however, Kevorkian believes that the user interface will emerge as an important differentiator for e-readers. "Being able to comfortably annotate documents and have those changes preserved after transferring the document to another device, like a PC, boosts the utility of the reader considerably in terms of conforming to usage preferences and the larger ecosystem of a user's devices," she says.

Plastic Logic's device will be able to store four gigabytes of data and will have a Wi-Fi connection, although Glass wouldn't confirm that it would support Bluetooth or cellular wireless connectivity. It will connect to a computer via a USB wire to transfer documents and recharge. And since the device only uses electricity when it refreshes a page, it can go for days without a charge. As with the Kindle, its black and white display is able to refresh in less than a second, but if the graphics on the page are more complicated or it needs to switch from portrait to landscape, it takes a little longer.