An Chinese source that would like to remain anonymous recently stated that the next iPad will be 3mm smaller than the current one. The height of the new iPad will be 239mm (from 242.mm) with the width being 186mm (from 189mm). This shrinkage will not be gained through a change in the screen size, but in a reduction of the bezel of the screen.
An artist rendering of the iPad speaker grille suggests a much bigger and presumably louder sound system.
This source has also made claims that the back of the iPad will be much more flat than it is now. I forgot how much the iPad wobbled on the table before I got my DODOCase, this being flatter would be a nice improvement.
Haven't heard much on the expected thickness of the iPad 2, but a 3 mm reduction is likely not possible with a current iPad thickness of 13.4mm. The Galaxy Tab is 12mm in thickness, but the PlayBook (where are these for xmas?) managed to get down to the 10mm thickness mark. With the expected additions to the iPad 2 in the coming months, making the iPad 2 10-15% thinner would be an accomplishments.
With these slight reductions in overall dimensions will definitely put a spark into the iPad Case market...I know that 3mm adjustment will make most cases unusable. My Muzetto Bag should still work fine with these slight adjustments though...