A co-worker lent me some of this to clean the rust off my sill plates. I snipped off a short piece of strip, about 2" for each plate, figuring they weren't too big, after all. I gave a fairly aggressive rubbing and now, after doing this twice, they look no better than when I started.

Don't know if I am using it wrong (i.e. too little), if the stuff he had was "old" or whatever, just thought I'd pass along my experience on this.