Play a multitouch HTML5 Tetris clone -- don't worry, keyboard will also work great: http://htmltetris.com
A huge fan of tmux, and I use Sublime Text and (more often) the indomitable Vim.
I have some special experience with:
- too much CSS
- animation, simulation...
- application security
- C++, template metaprogramming, applied clang c++ metaprogramming
- bunch more stuff I can't remember now
Why do downloads (storedownloadd) from the Mac App Store consume so much CPU?
~/Library/Developer/Xcode/iOS DeviceSupport/<iOS Version>/Symbols/System/Library consuming 14+GB of my Mac disk space