Under 11.04, the option to control the pointer with the numpad was set in the Hardware/Keyboard settings page.
How can I turn on mousekeys or configure them in newer releases?
In 11.10 and above you go to System Settings in the Power cog menu and select Universal Access.
Under the Pointing and clicking tab you will see a slider that lets you turn Mouse Keys on and off. The label says: Control the pointer using the keypad.
This procedure is the same from 11.10 to at least 14.04, and it is nicely documented on help.ubuntu.com. Because those instructions have been kept up to date, it's likely that the documentation will also be extremely helpful for future versions of Ubuntu.
Here are the links for mousekeys in versions 12.04 through 14.04 -- note that the url is identical with the exception of the version number:
Here are the 12.04-based instructions from the help site.
For Unity, I found it easier to hit the Super, type in the first few letters of "universal", then skip to the third step given above ("Select the Pointing and Clicking tab").
This is reflected in the 14.04 documentation: