Just as an aside, I would add that there are several Windows 7 tablets shipping now including the HP tablet (about $800), the ASUS EEE 121 ($969 or $1099) which just came out, and the EXOPC slate ($699)...and others.

Furthermore some UN-released, but supposedly soon-to-be-released devices include the Notion Ink Adam (its own proprietary OS, I think), the Motorola Xoom (Android 3.0) and the RIM Playbook (which seems to me worthwhile only if you are a Blackberry user since there is such tight integration).