I used to have a nice leather planner but switched to a Palm Vx a few years ago. (I know it's old but hey it works so why upgrade?)
1.) I have atrocious handwriting.
2.) Writing (for me) is somewhat painful, but I can type at about 50wpm.
3.) Transferring data from my computer to my Palm is as easy as copy+paste.
4.) I read my Bible every day. Carrying a Bible plus leather planner is a burden. Plus it has a nice searchable concordance which is great for looking up verses when, for example, engaging an atheist in discussion.
5.) If I would like to read something else than the Bible or play a game I can pop into Acrobat or Boxman.
6.) Paper planners (of the size I used to use*) can't be popped in and out of a pocket.
7.) Paper planners can't be backed up with the push of a button. What happens if you lose your paper planner, as happened to me once? My backups are also copied to a remote server in case of fire/hurricane/Technology-eating aliens from the planet Zotokry.
8.) Paper calendars don't beep when it's time for an appointment. I'd heard this from a bank president back in 2000. He said this was his #1 reason. It began me thinking, and when I missed two appointments, I switched.
* I have since learned of the Hipster and PocketMod.com PAAs (Personal Analog Assistants). Much smaller in size but not without the other restrictions. Not to mention the added burden of replicating the data to the next week's incarnation.
Paper feels good and clean and retro, but because the Palm OS is so well thought-out I can't see that I'm really missing anything. Just learned about DoodleBug so now I can actually draw on my Palm. OS 3.5.5 didn't have the drawable Notepad that the later versions did. Paper might even give some of you a "spiritual" feeling of retro simplicity but for me it was not worth the detractions.
Plus I still have options. I could certainly write on a piece of paper and later transfer to the Palm.
What reasons do you have for choosing paper over Palm?