I've used my PDA for years, and wouldn't know what to do without it. I use it for:
1) Calendar (with alarm to remind me of appointments)
2) Contacts
o my entire corporate phone book
o family
o friends
o business associates
o medical and other professionals
3) Task list (prioritized and dated, so I know what are the most important things I have to do, or deadlines that need to be met urgently
4) Clock (Keeps multiple time zones, so I know what time it is anywhere)
5) Alarm Clock, (with four pre-programmed alarms, so not matter what day of the week, I wake up on time, without having to change the alarm all the time)
6) Scientific Calculator
7) Expense Tracker
8) Map Program (so when I'm driving in the car, I can quickly get directions without having printed them out ahead of time from the internet)
9) eBooks (I read a lot, so I like to have an eBook that I can read whenever I have downtime, like waiting at the Dr.'s office)
10) Stopwatch (I use this for exercising, reading, anything where I have a set amount of time for a task)
11) Notes and memos (to keep track of important data)
And this mearly scratches the surface for you can do with a PDA!