Staying Sharp
amitt: Depending on how you're trying to exercise your mind, there are different options available:1) I tend to use google reader to keep tabs on several authors I find interesting.  I then make it a habit to find time to read a couple articles a day.  So in aggregate, I've actually read quite a bit and kept my mind from falling into a routine pattern.2) Someone else suggesting sitting in on classes.  I'll also say that depending on your location, there are like-minded folks that have meetups and tech talks.  These tend to be great opportunities for exchanging ideas and networking.3) Depending on what your open source contributions are, you may be able to shift the focus to something that you arent as familiar with.  There are OS projects out there that are heavy in math and physics that would provide challenges (3d game engines and libraries come to mind).  I tend to do side projects with a specific goal in mind when i want to pick up a new technology.