In fact there is a followup to this. Not only did the pen allegedly get the astronauts back from the moon, but the development costs for the pen have been recouped many times over (mainly by selling to enthusiasts on the earth), in fact according to Pedro Duque, the Russians use very ordinary ballpoint pens- they work just fine thanks! ;-)
The return from the moon story, which neatly cannot be corroborated, is that Neil and Buzz went for their parambulation on the moon and:
"When about to leave the moon, and the astronauts were climbing back into the Lunar Module, the life support backpack on one of the astronauts brushed against the plastic arming switch and broke it. The switch was to have activated the LM's engines for the module's rendezvous with the mother spacecraft."
The urban legend is that they undid a Fisher space pen and used it to activate the broken switch.
However, Buzz states that the pen he used was not a ball-point pen, but rather a felt-tip pen (see: http://www.hq.nasa.gov/alsj/a11/a11.posteva.html).