You probably didn't know this, but I mostly draw in Flash. I love the way it smooths my lines, knowing that I'm creating something that is vector, and the fact that it feels like a raster program when I'm drawing. Only problem is how limited our brush settings are. Above I describe an easy 2-step process on setting your brush up to have a sketchy effect.
Note: This should probably only be used for still images. A shit ton of objects would probably muck up an animation.
Also, I understand that the best way to get a sketchy look is to use phtotshop/open canvas/painter/pencil, paper, scanner/whatever else is your favorite drawing program. This is just an alternative for those (very few) Flash artists who create still images primarily in Flash.
Fun Fact: Tutorial created entirely in Flash (screen caps use masking and background is a multiplied movie clip)
Credit for crumpled paper stock: [link]