I always carry a pocket sized notebook and a pen with me wherever I go. It's still the fastest method to write something down, it always works and it's socially acceptable to use in all situations. Most people whom I meet, even in private, will see me take out my notebook at the beging of the meeting, taking notes occasionally while we interact. I don't think you could do that with a computer or phone and it allows me to remember important details and action points that I (and the person I'm talking to) would forget otherwise. At work I have larger, A4-sized notebooks that I use similarly.

One of the features that I appreciate most is that everything I write down is in chronological order and can be accessed very quickly. In seconds, I can go through last weeks notes and check if I forgot to do something, or even go back a year or more to revisit my thoughts on something that happened back then. Using a pen is also much more expressive, allowing me to highlight/format certain points as a discussion/meeting is ongoing and add illustrations, arrows etc. on the fly.

I've seen and tried some of the new epaper notepads and they're definitely getting closer, but for now they're still to slow, clumsy & fragile to replace paper for me.