Interesting article about efforts to bring home the remains of US service men who died in past conflicts: Killed in Action: Reconstructing Casualties - SPIEGEL ONLINE
With each passing conflict, both the number of deaths and MIA soldiers has been reduced, though. The majority of MIA cases are from WWII, followed by some 8,000 in the Korean War, 1,600 in Vietnam and about 125 related to the Cold War.
I found it quite surprising that 5x as many cases are from Korea, compared to Vietnam. Especially since the Korean War was much shorter, and less Americans served there. Apparently they got a lot better at recovering those KIA.