Today AppleInsider picked up a report from Kaufman Bros. that, over the last two years, Apple has purchased digital displays in 4 inch, 7 inch, 9 inch, 10 inch, and 12 inch sizes, and that some of these purchases were for a number of units appropriate to a small production run. While AppleInsider's report doesn't state outright that these were touchscreens, that is implied from the context.
In a separate development, Ars Technica reports finding yet another reference to an as yet unreleased iPhone OS device in the USBConfiguration.plist file distributed with an iPhone OS 3.1 beta release. That news shouldn't be public, but it is.
Meanwhile, Stefan Constantinescu contends that the Apple tablet device is a pipedream, one that will never come true. While his conclusion is looking like a long shot, he includes an interesting timeline of how the rumor of such a device has developed.
Given the various screen sizes that Apple has experimented with, I'm going to go a little further out on a limb and predict that the 2 versions of the Apple tablet device I've already predicted will be two different sizes, 7 inch and 10 inch, with the SMALLER of the two including the software-defined radio unit and being the more expensive (except as its purchase may be subsidized by one or more data service providers), as well as thicker than and approximately the same weight as the device with the larger screen.