All D3.js demonstrations in one document
docs.google.com
docs.google.com
The Google Doc is where the data is curated, and available for developers to make their own visualizations of the data.
I have read a decent amount of their documentation wiki, and have modified some of the examples, and made a few very simple things from scratch, but I am still missing some huge concepts.
Start here - http://bost.ocks.org/mike/join/ This gives you the neccessary understanding of how D3 works (from mbostock himself).
I found this tutorial to be pretty good -
http://alignedleft.com/tutorials/d3/
He also has a book out there with O'Reilly.
Here's another good one
http://2011.12devsofxmas.co.uk/2012/01/data-visualisation/
Hope that helps!
I humbly submit my own tutorial.
Also, happy to answer any questions you might have. Check my profile for my email.
It's awesome what they've done to showcase the community examples