"Eat your own dog food" is not an uncommon term in Silicon Valley. It means for a company to use the product they built themselves. If a company offers an email product to customers then they should also be using that same email product. It's not always easy to eat one's own dog food especially when that dog food provide a critical business functionality or is fairly new. Email, for example, has become vital for companies and they depend on it to be scalable, stable and reliable, but if you're eating your own dog food you might be using the pre-production version which might not be 100% stable or it's missing some functionality and which you need to build yourself. Because of this, even though many tech company talk about eating their own dog food, but don't really pull it off.
I find Google to be very serious about eating their own dog food. Everything released to the public is also used internally and this includes their APIs. Often companies release APIs but don't use them internally because they have direct access to the underlying technologies. Google does use their own APIs and during my first two months here, I've been learning a lot of the APIs in order to do my work. There are some amazing stuff out there and they are all listed at code.google.com.
Specifically, I've been learning the Google Data APIs. There is an amazing amount of access to APIs to allow developers to build sophisticated applications so I encourage everyone to try them out!