In reply to Jesse.

Besides the lack of transparency on features, there is also no disclosure of the server “map” that Jetpack is powered by. While a website and user base near Dallas (e.g.) might not see a speed decrease, 90% of internet users around the world probably will.

Sorry about that. All of the information is public, just maybe not easy enough to find.

Here are some links that hopefully help:

1) Complete documentation of the Photon API.
2) Photon source code.
3) Photon and other Automattic services are served from 21 different data centers on 6 continents and we continue to add more. The locations are all listed here along with a map. If you are interested in our level of network interconnection and more specific information about the data centers, you can find that information in PeeringDB.

While it's true that Photon does make your site faster by globally distributing your images and serving them from our servers, IMHO that actually isn't the primary benefit. The best part is that since Photon dynamically resizes the images on our servers, your images will always be served at the correct size, regardless of whether those sizes are stored in your wp-content/uploads folder. This can drastically reduce the number of bytes sent to clients - making things much faster, especially for clients on slower internet connections. It also ensures that if you switch to a theme that displays content at a different size, you don't need to "regenerate thumbmails" which can be slow or expensive (or both). Photon also supports some other nice features like transparently serving webp images to browsers that support it. There are other optimizations and features on the roadmap as well. We hope to share them soon.