I've just looked at dimple. It looks quite a bit simpler than implementing d3, I will have to play around with it, but from your experience how would you rate it in terms of ease of use, learning curve, performance, etc.?
It's pretty quick to get up and running with it, you can always get access to the underlying d3 selections to do more complicated operations, and the main developer is fairly accessible through stackoverflow questions or github questions. There are some gotchas I've run into but nothing that has made me consider switching. We evaluated a few different libraries before choosing it.
I can't speak for performance really because we don't have huge datasets. For ordinary business data (not looking at 1000s of points on a chart), it's fine.