When I open my system monitor and check the "processes" tab, I've noticed that regardless of what other apps I have running, "compiz" is always taking roughly 10% of my CPU. It might be a broad question, but what is compiz? I understand it's a window manager, but is it possible to use ubuntu without it? Is it a default application?
"Compiz is a compositing manager, which means that it enhances the overall user interaction by adding fancy effects to your windows, from drop shadows to awesome desktop effects like the Desktop Cube or the Expo view.
Compiz can also be a window manager, which means that it is the software between you and your desktop apps. It enables you to move or resize windows, to switch workspaces, to switch windows easily (using alt-tab or so), and so on." (source)
To run Ubuntu without, choose "Ubuntu 2D" on the login screen: