The amount of information about the system in this area is amazing.
For example try out these commands
cat /proc/cpuinfo cat /proc/meminfo cat /proc/version cat /proc/uptime cat /proc/loadavg cat /proc/net/dev
When scripting you will probably want to use the info in a more digested form. The command for a script could be something like
cat cpuinfo | grep vend | cut -d' ' -f2
A useful debug trick is to determine what the environment settings where for a process after it has been started. To do so you would cat the processes environ file like so;
The /proc/sys directory can also be used to alter certain files in a live system to adjust the kernel system wide. To tell which files can be altered just ls -al and look for the writable bit. Keep in mind that changes made in the area are temporary, and some changes can easily kill the system. To make the changes permanent the /etc/sysctl.conf needs to be edited.