"I am posting this from mine. (Palm One Treo 650)"
I don't know how I lived without my Treo.
Instant access to google or any other research source. I was at a store and price matched another with their website by just pulling it up. Comes in very handy.
I keep current work project info on it in MS Word, Excel, and PDF format.
I have SSH, Telnet, VNC, Windows Term Server, FTP, Ping clients installed...
...and It synchs with my outlook schedule. I can record voice memos, video, or still photos, too.
I have a 2gb SD card in it with about 1.5GB of MP3, and I can also stream shoutcast with it.
I travel a lot, and it's VERY convenient to have all this stuff in one small package.