I am glad to see this on the HN front page - excellent overview of graph theory and interesting ideas for using data flow and also a common API for several underlying graph datastores. The first part that used matrix/tensors to explain different types of graphs and operations was good also.
Btw if youre further interested the authors other papers are listed at http://markorodriguez.com/Lectures.html . Bonus you dont need a slideshare account to download the slides pointed to by this story.
Check out the tutorial: http://networkx.lanl.gov/tutorial/tutorial.html