There have been some tremendous advances in these digital books. Although they still have grayscale screens, they are becoming increasingly popular. Built-in Wi-Fi, 3G, touch screen, illuminated screen, MP3 player, photo book. All these features remind me of my old Apple Newton Messagepad. That thing was a great little device.
The biggest advantage of a grayscale screen is that you save considerably on battery life. However, everyone is predicting that these e-book readers will eventually get color screens. Then, the line between a tablet, a MID, and an e-book reader will get seroiously blurred.