(As Far As Eye Can See) Research published a report called "Developments in e-book, and e-magazine reader technology", which covers the current and future development of e-publication reader technology between now and the end of 2008.
Nick Hampshire and Guy Kewney, the two researchers of the report, maintain that just four years from now e-books will be so well established that a typical price for mobile hardware will be less than US $35. They justify their (rather optimistic!) assumption of a growing need for e-book technology, 1. on simple economic grounds, such as the delivery of up to date text books to every one of China’s 165 million school and university students, and 2. on the need for new revenue sources, as is the case with the consumer electronics industry, or, crucially, the mobile phone companies.
They also looks at how these devices will evolve over the next few years by examining developments in key areas of technology. Interestingly, PDAs don't have a bright future, at least according to the report. Instead, the researchers claim developments in mobile phones to be the future main drive for e-book technology. The following graph depicts their projected growth in annual sales of devices capable of functioning as e-book devices:
A summary of the report can be downloaded from Afaics's hompage