Paper versus Pixel
People who know me know that I am a proponent of the paperless office, and even the diskless office (aka. the cloud office, which involves using a combination of software as a service and cloud software for everything). I use a variety of tools to achieve this, Google supplying a large amount of these, and Mozilla a key one with Weave.
However, in writing my thesis, I had to switch to paper for the mathematics / game theory model. It was just that much quicker to write new equations and solve them. While limited, paper for math certainly is more agile.