I have for reading original sources. Not just knowing that so-and-so gets credit for doing something, but looking back and seeing what that person said in his own words. I think it's a tremendous way to improve your own skills. It's very important to be able to get inside of somebody else's way of thinking, to decode their vocabulary, their notation. If you can understand something about the way they thought and the way they made a discovery, then that helps you make your own discoveries.
Knuth
