Here's my approach - if I feel like using paper, I use paper (moleskin notebook, scrap, printouts). If I feel like using my PC/PDA, I use that.
However, everything that could be valuable that was input on paper (the results of planning/brainstorming - not the notes themselves) eventually gets input on my PC (scanned or typed). This information is either input during my weekly review or marked for input at a future time.
I almost always input calendar items and contacts directly to my PDA. Furtuer tasks usually make themselves apparent throughout the day/week and are input in my PDA/PC throughout the week.
I used to fret the paper/pc combo, but allowing myself to switch when I want, knowing that my data will eventually all make it into my digital archives, has given me a refreshing sense of freedom. It has also allowed me to put more focus on the content of my weekly review and less on the structure/format/software-of-the-week..