Does anyone know of a cel shading plugin for Final Cut Pro? I'd be interested to see what it looks like and whether it would work (in moderation) for my film.

Yeah, haven't heard of anything. You could try experimenting with exporting a quicktime with 16 or 256 colors and then reimport it and tweak it from there. But I don't know any tried and true way that isn't labor intensive.

Maybe doing a Gaussian blur, then reducing the color depth, then sharpening. This is all just brainstorming, but maybe it'll give you an idea.

I know there's a technique involving duplicating the layer, blurring it, and using one of the layer blending modes. Just play around.

There's no really good way to get that look through an automated process. 'Waking Life' ended up using specialized software and it still entailed a lot of rotoscoping by hand.