"Scented with peppermint oil and infused with caffeine anhydrous, each bar of Shower Shock contains approximately 10 servings/showers per 4 ounce bar with 250 milligrams of caffeine per serving. No, we're not kidding and no you don't eat it. The caffeine is absorbed through the skin..."
Interestingly, ThinkGeek also notes that "We Cannot Ship Any Caffeine To Sweden Or Belgium". I suppose that if your caffeine resistance is so high that you need a bar of soap to get that buzz, there's something desperately wrong.