The Terminal in OS X is, for most people that don't need a command line interface to OS X, not all that useful. But, because it's an entry to the core of OS X, there are tons of commands you can run to tweak all sorts of different things on your computer. Change the Dock location, turn off Mountain Lion window animations, show hidden folders and settings. The list goes on and on, and many of these things are useful to the typical geek. And you know what all these commands have in common? They all start with "defaults write".
The clever @defaultswrite account tweets another great "defaults write" command every day or so. Not that you would find all of them useful, but you may just find the solution to some OS X nuisance every once in a while.
Just don't forget to run the "killall Dock" command after you run the "defaults write" to relaunch the Dock and enable whatever tweak you just made.