For one thing, I suspect you never had...
-- A web browser.
-- A PDF reader
-- Wireless networking
-- Street Atlas USA/MS Streets & Trips or similar with a street-level map of the entire country (including all the Wal*Marts and Dunkin Donuts) linked to a Bluetooth GPS receiver
...and plenty of other everyday "necessities" that people with laptops expect today.
I think a Nokia N800 with one of those small Apple bluetooth keyboards very much would meet all the hardware needs you have, but unfortunately there's probably some software that you'd want to use that doesn't exist for it. Plus the screen is probably a little small for, e.g., CAD work...
---Joel