Where I work, a certified tech earns the same amount as a tech w/o certification in the same job title. However, my employer pays for one sitting of the exam and a $1000 bonus for passing it, and certified techs do have an advantage when applying for a job or a promotion. The cert does add to a tech's credibility.
According to the U.S. Bureau of Labor Statistics the estimated mean annual wage for a pharmacy technician as of May 2008 was, $28,500. This would amount to $13.70 an hour.