I always lock mine now since after I came out of the mall one day and realized driving home that my tailgate was down. I may have came out just as it was in the process of being swiped.

 

I've had my 04 for three years and never bothered to lock it, after working a 14 hour day yesterday I came out to find my tailgate missing! only ones on ebay right now don't include hardware and go for $185+$55 shipping. any ideas where to get a fully loaded tailgate cheap?

 

I got one on e bay fully laoded for $250 shipped. I had my originnal one keyed badly and was cheaper just to replace it that way (same color). You might try craigslist also. I found a bumper for my sons ranger that way. You have to search each city in the US but not hard to do. They have an auto parts section. Either that or try the local salvage yards.
On mine I wired up an automatic tailgate lock in conjunction with my door locks. Very cheap mod, takes a cpl hours but each time I lock my truck I know that the tailgate is locked also.