The shortest commercial airport is Juancho Yrausquin Airport Saba, Netherlands Antilles, 1200' long. Cliffs on both ends dropping into the ocean, no overruns. There are several YouTube videos of it. Been there once, in a fully loaded Twin Otter, its a no bulls$#t landing at 12,500lbs, but the pilots do it safely every day. What an awesome plane, and pilots.
http://www.georgiajets.org/Links/FWIW/S ... rport.html
Of course I think the most impressive airport used for daily commercial service is Lukla Airport in Nepal by DO-228's and DHC-6's. 1600' long with a 12% slope at about 9400MSL. One way in and out, with a 2000' drop at the end of the runway, that will help if you are not already flying.

Mountains immediately surrounding the airport rise thousands of feet. Planes crash there every few years. Most recently on Oct. 6, 2008, 18 people were killed in a DHC6, the pilot survived. I would hate to have been him.
http://www.youtube.com/watch?v=DqgZvb37 ... re=related
I think that Highlander that rolled down the hill without the engine running takes the cake for shortest "unimproved" strip. He used it more than once.