One of the first things I do in any new installation is add a system monitor to a panel I can see all the time. I like to know the instant my system resource utilisation changes.
Under Unity, the ability to add items to the top panel isn't immediately obvious, but the solution is nonetheless simple:
# apt-get install indicator-multiload
$ indicator-multiload &
New readers: in code extracts, # signifies a root shell and $ signifies a user shell. In practical terms, what this means is that when a line begins with #, use the command sudo to temporarily become the root user. You may be prompted for your password after doing so. For example, in the case above you would enter:
sudo apt-get install indicator-multiload
Note that there is a bug in the present version whereby the CPU "nice" measure accidentally shows the CPU "system" measure, and vice versa. A bug has been raised, and by using a newer version from the ppas (details in the LP entry referenced) you can avoid this problem. Alternatively, just switch your colour selections for the Nice and System measures.