Well done! I actually was planning on tacking this one myself using svg filters but I've been too busy. I didn't see Mike Bostock's comment suggesting the custom line interpolator and wasn't aware of it -- d3 is gaining some cool new functionalities!
Thanks also for the great references. In spite of being a big proponent of d3, I somehow missed the "Toward Reusable Charts" piece Mike wrote earlier this year, which succeeds where I have struggled. I've been using the standard prototypal approach to creating reusable and easily configurable charts, which can be cumbersome for the caller. This functional approach with closures is so much cleaner and more reusable. It's the only way I'll make my d3 charts from now on!
Thanks also for the great references. In spite of being a big proponent of d3, I somehow missed the "Toward Reusable Charts" piece Mike wrote earlier this year, which succeeds where I have struggled. I've been using the standard prototypal approach to creating reusable and easily configurable charts, which can be cumbersome for the caller. This functional approach with closures is so much cleaner and more reusable. It's the only way I'll make my d3 charts from now on!