Useful for understanding the relationship between data and the graphic representation in d3.
http://mbostock.github.com/d3/tutorial/circle.html
This seems to be the key to working with d3.
http://bost.ocks.org/mike/join/
There are loads of examples if you check out the source. Mining that for useful techniques is worthwhile.
https://github.com/mbostock/d3/tree/master/examples
Takes you through drawing a chart -> dealing with/animating data changes:
http://mbostock.github.com/d3/tutorial/bar-1.html http://mbostock.github.com/d3/tutorial/bar-2.html