@kentuckycat - I've seen a wrist watch PDA, but I haven't had a chance to play with one.
From what I saw, it is basically an LCD screen with a few icons that you can select (calendar, phone, addresses, etc.). Unfortunately, I didn't see one that had a browser. I agree with you, though, that it would be quite the small screen.
I don't see this becoming the latest craze, but I can see watch phones and PDAs becoming one of those things that are worth a lot of money to collectors in the future because of their rarity.