The mistakes in our genome make a stronger case for evolution than the bits that are right. In essence, a common designer may have designed different creatures with the same "right bits", but why would an intelligent designer have put the same mistakes in two independently designed creatures?

I like the analogy with cheating. If two papers have the same mistakes (misspellings, odd grammatical errors, etc.), it is a pretty safe bet that one was copied from the other or they were both originated from a shared source.