Raspberry Pi Car Speed Detector

Is it practical enough that you could do anything with it, like give it to the police for a citation?

Or is it just awesome in a nerdy sort of way?

I would think that it's just awesome in a nerdy sort of way...the programmer could just fudge the numbers and output an incorrect reading, to screw with someone they didn't like for instance.

Plus I don't think promoting vigilantism is a good thing.

Good point but definitely nice to have something credible to have a discussion about the jerk driving 75 on your 25mph street.