The Mobile Internet Device (MID) sits between cell phones and UMPC's. Forward Concepts projects 300K MIDs will be sold this year, most in the 3rd and 4th quarter with perhaps a couple of dozen new devices on the market. The important e-book related properties of a MID (as defined by Forward Concepts) are: 24-hr battery life, VGA 4"-6" color touch LCD screen, $300-600 low-mid price range. I'm not sure that even one device on the market today meets this criteria, with the Nokia N8X0 and perhaps some Windows Pocket PCs being closest.
For more details, see UMPC portal's
Moblin, Millions of Netbooks and a strong position for Atom. and Electronics Supply and Manufacturing's
Interview: Will Strauss of Forward Concepts on Mobile Internet Device (MID) study.