Thanks for taking a look!
There's a little more info in our recent blog post about this too: http://bits.shutterstock.com/?p=103
In particular, here's an example where you can switch between stacked, percentage, and line views; toggle on and off each data series; re-order the stack with drag-and-drop; zoom in to a time slice; add smoothing; add annotations, etc:
http://shutterstock.github.com/rickshaw/examples/extensions....
It can make a difference, having this functionality around when you're trying to dig in and read your data.