I just added my site to Blogdex, which basically tracks what links everyone is propagating on their blogs. Right now, the number 2 link on Blogdex is to a page featuring caffeinated soap. Supposedly, the deal is that you absorb the caffeine through your skin while you use it.
Now, I'm as much a caffeine enthusiast as the next person, but I don't know about this. My showers tend to be pretty long as it is -- I'll think about stuff while showering, or just let my mind wander. I could just see myself spending even more time in the shower trying to get a buzz off my soap.