I'm getting the wrong kind of spam. Mine are mostly irrelevant comments that link back to useless websites that probably give my PC viruses. However, I get your point and it's an idea to keep in mind when you do get some "useful" spam comments.
I never find a decent site out of spam comments I've received. All those spammers are promoting sites that are of the lowest quality possible.
This might be a good idea, and i should definitely try this method. Found another "good method" today.....lol