Read all about it: http://www.care2.com/causes/five-years-of-reasons-to-microchip-your-pet-2.html
Excerpt:
Without a microchip, Bandit and Mike never would have found each other again. Time Magazine writes that “approximately 10 million pets that have been chipped over the past 15 years.” They “have helped reunite more than 600,000 pets with their owners,” reports Petside.com‘s Lavanya Sunkara. For a FAQ about microchips, visit the Humane Society‘s website.