All my notes (of which there aren't many) are kept in text files in a well known directory, along with all my code. I can grep for things I've solved or thought about in the past and get the information instantly. And since it's electronic, I can back it up, copy it, and access it from anywhere.

The only times I've found myself needing paper is when dealing with graphics programming, in which case it's simply for figuring out the best way to tell the computer how to do something. Once it's in code, I don't need the paper anymore; I can just grep for it.