It's worth noting that Amazon's PDF reader lacks a zoom function which makes many PDFs entirely unreadable on the device.

ENGADGET: Kindle 2.3 software update available, generation 1 owners need not apply

Google's Gmail currently lacks a calendar function, and some believe the firm would like to add one - albeit perhaps a limited version that could serve home users well without meeting the requirements of corporate users, thus avoiding a head-on challenge to Microsoft's business model.

BBC: Analysis

The Irex also lacks a Home button, a note-taking function, any way to highlight text and a built-in dictionary.

WSJ: A Review of the Irex E-reader