This past February 2009, Applied Cognitive Psychology of Wiley InterScience published Jackie Andrade's findings about doodling. With a group of 40 people, she tested the impact of doodling on concentration and memory. Participants were asked to listen to a boring telephone message with names of people as well as some irrelevant information. The doodling group was given paper with shapes -- alternating rows of squares and circles -- and the control group was given lined paper. The doodlers doodled, the control group didn't. In the end, the doodlers were found to have 29% better recall of the names than the non-doodlers.
Citation: "What does doodling do?" By Jackie Andrade. Applied Cognitive Psychology, Vol. 23, No. 3, Feb. 26, 2009.

For more on doodling: 
 

Read/hear NPR Morning Edition story on Doodling
Read Andrade's paper, What does Doodling Do?
See also: Sketchy Brain Booster