I have one. It is my long term memory. If I didn't have a PDA I would be sacking groceries somewhere (some might suggest that is the best use of my planning skills ). It allows me to remain employable. However, I only use if for dates and phone numbers. I don't utilize it to its fullest. Do you use one in your work?
PDA - Personal Data Assistant i.e Palm Pilot, Handspring Visor....
I use a Palm M100 ($130) and Microsoft Outlook XP, both at work and at home, to keep organized. My wife and I email each other our dates and keep a semi-common contact list. It works great and I rarely miss something important. I am so dependent on the system I keep a CD-R back up of the data in our safety deposit box. I have about 2000 active contacts and my digital schedule record goes back to 1999.
I used to keep the regulations I worked under on it. I loved quoting from the regs or law to a contractor/developer while in the field. They didn't see it coming - ever.