"Find out what’s your “Doodle Score” in 6 x 3 different playing modes! You’ve got 6, 12 or 18 seconds to draw a line with your finger. When the time is up, your doodle will be scored depending on the playing mode that you selected.
These are the playing modes:
Most Crossings: draw a doodle that has as many crossings with itself as possible.
Most Regions: draw a doodle that divides the white area into as many separate regions as possible.
Longest Line: draw a line that is as long as possible.
Longest Line, no Crossings: draw a line that is as long as possible, but doesn’t cross itself.
Composite Score: this is a combination of the first three playing modes.
Small Regions: draw a doodle that divides the white area into many separate regions. All regions should be as small as possible.
Doodle Score is OpenFeint enabled, and also uses Game Center on the newer iOS versions. Leader boards and achievements worth 800 points are available on both services. After you played a game, you can always send the result as a challenge to one of your OpenFeint friends. For best results, we recommend that you allow Doodle Score to send you notifications."
Source: The Developer Website.