I'm not worried about DFW at all, although the reintroduction of more interstate service at Love may take away some of their traffic. I look for DFW to eventually take over from ATL as the busiest airport in the world.
As for MIA, as the population of South Florida gets more and more spread out, airports like FLL and PBI will be busier, while MIA will probably stay rather flat.
I can't comment on PIT, although they're pretty much at the mercy of USAir. I will say that major hub airports (with a one-carrier vast majority), such as PIT, CLT, STL, etc have it a little tougher because of that airline's majority, while other dual hubs can use that advantage, and combine with the spoke services of the rest of the airlines, to maintain a decent level of growth.
Tom in NO (at MSY)
"The criminal ineptitude makes you furious"-Bruce Springsteen, after seeing firsthand the damage from Hurricane Katrina