Scott Murray, author of Interactive Data Visualization for the Web, has just released a 3-hour video tutorial about D3.js through O'Reilly. He has also written an article to present it: '5 Reasons to learn D3: D3 doesn’t stand for data-design dictator.'
I have just purchased the video and I'm planning to watch it this same week. It's been offered with a 50% discount until May 22, so you better run if you're interested in improving your visualization skills.
To learn more about this library and see other articles, books, and free tutorials, visit: 1, 2, 3, 4.