Arizona State University Study:

Consumer attitudes toward restroom advertising were found  to be very positive with as much as 98% generating a favorable reaction.  

Rice University Study:

Retention of impressions generated by adboards were found to be an average of 40% stronger than by other media. Also, thatthe unusual and unexpected nature of the form of advertising "commands focal levels of attention" thus enabling better comprehension and longer lasting impressions.The Rice University researchers timed 1000 people while in restroom, and found an average of 1-1/2 to 2 full minutes were spent in front of adboards.   

Barbour & Monroe Marketing Research Studies:

Found as much as 98.9% of restroom adboard viewers reacted positively or neutral to seeing ads in restroom facilities

All three studies concluded:

That the ability of the adboards to target certain groups by age, sex, income level, or lifestyle is one of the greatest strenghts of adboards over other media available.

Market Intelligence Media Research:

When adboard viewers are shopping for a product or service, retention of that product or service advertised raises to an impressive and effective 85% retention rate.