Even if you aren't using an application, if it was a window on the screen or in the dock, it's going to get redrawn. Whenever the screen gets updated the OS is going to ask the app to redraw it's window. Therefore it will hang around in memory, or get swapped back in from disk.
OS X's...
Got me a CS phd, cause I'm a teenage lobotomy.
I do research in computer graphics / medical visualization. Basically how to use 3-d graphics for medical imaging & surgical planning.
The cool thing about OS X is now I can do all my work on one system. Before I'd use big SGI's for hacking...
Another useful way of navigating are the commands pushd and popd.
The following command pushes the current directory on a stack and changes to the new one.
pushd /Volumes/blah/whatever
Then you can pop current directory off the stack with:
popd
To see the directories use
dirs...