I've been a user for 8 months or so, and I find my major apps are:
1) Appointment Calendar - not a lot of time spent here, but very useful for scheduling, alarms, and expense reporting.
2) Contact Manager - again, not much time, but really handy when you need to call someone from the car.
3) Password safe - VERY useful when you have dozens of e-mail, FTP, vendor, etc. passwords. This is the killer app for me - whether I'm at home, at the office, or on the road, I can track down the most obscure username and password. Not long ago I was in the car, hundreds of miles away, when someone in the office desperately needed a password. No problem...
4) AvantGo News - in terms of hours spent, my biggest app, albeit one of low priority. Saves me 50 cents every morning by substituting for buying a newspaper to read with breakfast. It also provides a great filler when caught standing in line (on line to you NYC-types), waiting for an appointment, etc. I get news from Reuters, Bloomberg, MSNBC, the NYTimes... free!
5) If you are a game person, there are some very decent timewasters available. Good for airports after you have maxxed out your news intake.
It's safe to say that I'd be reluctant to give it up...