I’ve been able to generate newspaper-style navigation that works on all non-touch Kindles, but the Kindle Touch and Kindle Fire use new periodical-navigation formats that I haven’t been able to successfully generate yet. I don’t know if Amazon will ever make this possible. And recent changes to Kindle “personal document” storage makes it difficult to delete old Instapaper articles from the Kindle Touch.
He also says that the Kindle Touch is slower at page-turning than the Kindle 4 (and Kindle 2 and 3). I have the Kindle 3 (a.k.a. Kindle Keyboard) and am not at all tempted to upgrade. The Touch lacks page-turning buttons, and the Kindle 4, though a bit smaller, would be significantly more unpleasant for type-to navigation and entering short notes.