[aw3c2]

If you want to make graphs like those on their page, it's fun. But once you want more it can be super annoying and hard to understand.

[bshimmin]

Yeah, my experience exactly. It's a great start if you're prototyping and your initial use-cases map well to their demo pages. Once your designer gets excited, you'll have to write a lot of code on top of it and may well consider ditching it entirely.