Gruber wrote this. Then Marco wrote this. Then Siracusa wrote this. And finally (maybe), Marco has written another article which I think comes to some very nice conclusions that I agree with:

The Tablet is Apple’s chance at applying the lessons learned on the iPhone to a device big and versatile enough to be a low-needs user’s only computer, or to be the only computer that a power user brings while mobile (as Gruber suggested) instead of a laptop. It can be the computer that we buy our parents or grandparents without worrying that we’re signing ourselves up for years of painful tech support calls as they “lose” documents by saving them in the wrong folder, think they can’t save any more files because the desktop is full of icons, delete their browsers’ icons and tell us the internet is gone, keep five different antivirus products half-installed, and fill their RAM with programs they never Quit because they just close every window instead and don’t notice the tiny “running” dot in the Dock or know what it indicates.

I highly recommend you read the entire thing.