James Polits has an After Effects tutorial video on using the Scribble effect and the “rd_ShapesToMasks” script from Jeff Almasol's Redefinery, Sketched/Scribble Text Tutorial Using After Effects CS3:
"Ever wondered how people make that scribbly filled-in text? I used to wonder how to create that look, but never found a tutorial for it. So I decided to make one. This tutorial will walk you through using the Scribble effect and the Write-on effect in After Effects CS3 to create this cool and handy animated text look."