I'm another one of those that uses both mediums.
You can never go wrong with pencil and paper, but sometimes I just get the itch to fire up the computer and type away. Initally, I was using Word, but I've begun looking at PCGen, and will be taking a look at Keynote.
An interesting thing that I've found out about myself: Whenever I try to take notes on my computer, I tend to wander and not focus on what I'm working on. I'm getting better about that, I think, which is why I still use pencil and paper (and yes, I do use a pencil; I've never enjoyed writing with a pen. Don't know why), but I hope that one day I'll be able to keep my focus when I'm working on the computer.
Another thing: When I was growing up, there weren't all that many computers around (at least where I grew up), so anything that I wanted to write had to be done long hand. When I got into high school and had to do term papers, I was able to type them up on my dad's Commodore 64 and print it out, but it took too long for anything else (dot matrix printers and all that). He also had a Texas Instruments something-or-other, but we mainly used that for video games along with the Odyssey (anyone remember those? KC's Crazy Chase rocked!).