I'm on my 3rd PDA. First was PalmIII, then Handspring Delux, now Sony Clie' PEG-NX60.
I'm a mechanical engineer, and I love all the apps that I can load into it. I like that I can play/give PowerPoint presentations, check/send email (with wireless card), play videos, etc, etc. I find Grafiti to be faster than the QWERTY keyboard.
If you are not an organized person to begin with, or do not have a heavy schedule whee you have things sheduled every 30-60 minutes where you have to realy manage your time, I don't think a PDA would be a good fit.
I will say that it is a pain to carry both a PDA and cell, and a combination of the two will be my next purchase, but not for at least another 2 years.