The Powermat experiment at Starbucks appears to be going well. After rolling out the wireless tabletop charging stations to a small sample of locations in Boston, Starbucks is expanding the "evaluation" to select Silicon Valley stores. "We have seen positive customer response to wireless charging through our tests in Boston, and are pleased to now extend this experience for our customers in the Silicon Valley area," said Adam Brotman, chief digital officer at Starbucks.

Pleased as Starbucks may be, the Powermat experience remains largely inconvenient for consumers. Virtually all of today's popular smartphones still require a case or, even worse, a portable battery to achieve compatibility with the system. The Power Matters Alliance has enjoyed some momentum in recent months (led by this Starbucks deal) but the competing Qi standard has already made its way into shipping devices — including the brand new Nexus 7. You won't be able to wirelessly top off Google's latest tablet at Starbucks, but for those who have already invested in the Powermat platform, a full list of charging locations can be found below.