Many people doodle, especially during class or meetings. Not just artist-types. It could be because doodling actually increases attention. To learn more, click here.
There's also a TED talk on the subject:
If you want to take your doodling to the next level--using doodling to create art, then look for this book the next time you visit: Doodles Unleashed: Mixed-Media Techniques for Doodling, Mark-Making & Lettering by Traci Bautista [741.2 BAU].