smartyshorts:  I have to respectfully disagree.  I'd never heard of the Coke thing until this thread.  Our apartment block has very rusty water b/c they're too cheap to put in new pipes.  I have used every bathroom product known to man to get the rust stains out of the bottom of the toilet.  The other night I poured some Coke down there and let it sit overnight.  The next morning........voila.....gone.  Scary to think that we actually drink the stuff!