I think they are very useful if you know how to use correctly.
you can do soooo many things with a PDA, not only for business, but for entertainment as well (games, aim, movie, internet surfing, and etc)
With the internet surfing, you can be on PF all day long. heheheheh.
many pda comes with a camera, so you can snap a photo and send it directly to your email and print it out when u get home.
Im sure many pda's come with a expandable memory slot for the memory card, so transferring images, contacts, and agendas to your computer is alot easier if you have a later computer that has a memory card reader... with that being said, NO usb data cable or infrared will be needed. ummmm.. AND YOU can use your pda as a cell phone and an MP3 player... and yada yada yada yada. hmmmmm. ok. lolz
But of course, I always perfer my good ol scrap book which i put alot of post it notes and written random reminders and thoughts all over the pages. lol. hahah