Rather than me going on about it here and poorly describing the excellent detail within, I'm going to redirect you the .Net Rocks! episode released yesterday (a tad serendipitous if you ask me) in which Mark Miller talks about his experience and learning from Tufte with which I can only agree.
Enjoy both the book and the podcast! I know I did.
(I recommend that you are sat by your computer when you listen to the DNR episode; with your Shrinkster links ready to go, Mark fires them off thick and fast).