the benefit of pens vs. pencils (especially for young writers) is spot on. I've always preferred writing with pens to pencils, but never stopped to analyse why. Which is a bit crazy because the contrast and consistency comparisons are hardly rocket science, they're just so 'normal' to us that we don't bother to think through why we prefer one over the other.
For 90% of what I do, I prefer writing on the computer. However, when it comes to doing flash writing assignments for writer's group, I'll chose a pen over a pencil any day. Write, baby, write, and go back and edit later!