Hardcore Linux users will tell you that copy and paste is as simple as selecting a piece of text and middle clicking. And if you’re stuck with a two-button mouse or trackball, the usual trick is to click both left and right buttons simultaneously. This used to work out of the box on Ubuntu, but recent versions (since at least 11.04) do not have the middle button emulation.
What to do? – Install this cool little program:
sudo aptitude install gpointing-device-settings
Then run it and check the middle button emulation box.