Absolutely yes. As already mentioned the calendar and contacts lists. Everything is in one place. Yes, you could use a daytimer booklet. But, how do you sort through contacts to find a category related to just one business? That alphabetical paper address book won't do that. Plus, everytime there a change you have to white out the paper to make the correction. Which is messy.
Taking notes on your PDA allows you to save it electronically. If you take notes on paper, you then file it someplace in a folder or cabinet. Six months later you need to find that information. Now you have to sort thru and re-read six months worth of notes. I take meeting notes on my PDA and upload them to my PC. If I need to find some information the computer search function will find it for me. :approve:
Part of being "more productive" is taking breaks. My PDA can provide some diversions to take my mind off work. Especially when working on a short deadline. :)
A PDA is a tool. A properly used tool can make you more productive whether it be for business or pleasure. :)