Nice visual directory layout
http://www.aclab.ca/wiki/images/7/70/Linux_Directory_Structure.png

The /usr/bin and /usr/local/bin can be confusing. Like I said in the google wave, according to proper linux standards, ALL custom user installed applications should go into /usr/local/... but this is a standard that all the linux programs have not followed, almost all programs (besides the base) on your system will be in /usr (/usr/bin, /usr/sbin) not in /usr/local/. This chaotic mess of application development is one reason I like FreeBSD so much. FreeBSD is unix, nearly the same as linux (different kernel), but FreeBSD was engineered by college students, while linux was chaotically "grown" from the community. So FreeBSD enforces every standard possible. On a freeBSD system, absolutely every program will be in /usr/local/ folders.

A great command we have not discussed yet is the 'which' command. Typing 'which' and then the program name, like 'which wget' or 'which firefox' will show you where the program is located, on linux, if it's not a base system file, it will most likely be /usr/bin or /usr/sbin.