This article discusses how to prepare and maintain a jack o' lantern.  I haven't tested out the suggestions, but, the part of the article that has the most potential for me is the use of hairspray to help preserve the pumpkin after it's carved.  You may not be willing to soak the pumpkin in bleach or water and wrap it daily as suggested, I'm certainly not!  But, using vaseline or hairspray seems like an easy way to get a little extra life out of a jack o' lantern.  I've seen this suggested in other articles also.  When I replace the jack o' lantern that's currently fading fast on our front porch, I'm going to give the hairspray a try.