Thanks for the input.
No, I keep my calendar on my computer and my task list there up-to-date religiously. I do HORRIBLE with "regular" hand-written calendars, etc. I really like doing the calendar electronically. Let's say you sent me an email inviting me to lunch at a specific place tomorrow and you included directions along with names of people who would attend. I would just drag the email to my calendar, your written directions and all, and the directions and everyone's names (because I'm horrible with names) would be there in my calendar both for use in the present and to refer back to. Of course, in the "old" days, I used to print the email and paperclip it to the page the date is on, but then my binder got to heavy to carry.
In that case, you're well suited to the use of a PDA, and you'll probably benefit from a smart phone.
Focus your efforts on features that make keeping your smart phone up to date convenient and easy. Bluetooth is probably the most convenient wireless method of linking and syncing a PDA.
If you're on the road a lot, one other option you might consider is checking to see if your date book and address book software allows you to publish the information to a web site where the latest information can be accessed using the PDA's web browser. Naturally, you'll want to make sure that the information is password protected. Between sync'd data and the web published data you should be up to date all the time.