I'd strongly urge you to never build anything on top of a Google product or platform. Ever. Always look for an alternative. There's some exceptions that feel safe like Golang or NaCl but anything that isn't in Google's core products (search, ads, chrome, gmail) is subject to cancellation, API breakage, and general shittiness; especially for customer support. Even paid stuff, like Google Site Search was recently announced as cancelled. Please don't ever use Google products, you'll just encourage the constant rise/fall tide.