I use the notes a lot, store my passwords, some URL's, helps me keep track of stuff like wife & kid's SS #'s, DL #'s, model #'s of lawn-mower, tiller, all that crap that I forget when I'm @ the store & stumble across parts that are model specific.
Address, phone #'s are handy too...
I also like Avantgo, when I get a quiet minute, I read AT hardware articles, WSJ, NYT, etc...
Have gotten so accustomed to using it for a reference, that I'll retire my Casio data bank watch when the current one dies & start wearing my Rolex
I had a couple of IPAQ's & went with a Palm 505 because of the size, I use it like a billfold with the case I have, keep my driver's license & CC's in it...