I've done a ton of work with Chartserver, and I'm continually impressed by how elegant it is in every detail of its implementation. Although, I'm also a huge fan of D3. Not every chart should be built in JavaScript. I can embed it, I can drop it in an email, I can serve up 20 charts on a page in milliseconds, and I can do it equally quickly anywhere in the world.

Services like this, are one of the things that keeps up 'Google's not just in it for the money' cred, I'm going to be really sorry to see it go.