"On the average, people go to the bathroom 6 times a day. Public restrooms are used very often. Why not place your business or product in front of thousands of people who use restrooms every day. This is a sure fire way to grab people's attention." Just Toilet Paper. 500 sheets per roll, $12 apiece.
On the one hand, there are certain brand equity issues. On the other hand, your message does get undivided attention and perhaps even second-hand readership.