There are laws in place that specifically handle writing bad checks. While I'm sure double-spending Bitcoin transactiosn is illegal in some way, it is probably covered under a more nebulous fraud-type statute.

I'd be curious to see the percentage likelihood on both, as well, as I suspect they are very different. Would businesses accept checks if half of them were bad?

The general fraud crimes you would get convicted of have a pretty nasty set of penalties. But good luck convincing a federal prosecutor to care about $20 worth of online goods that can be revoked.