You need to use a cute girl's picture as your avatar if you want answers.
Let's take a guess:
United, US Airways, Delta, Northwest, American, Continental: hard to say right now. All are stagnant for obvious reasons. In the past, anywhere from 5 to 15 years.
America West: 4 years, give or take a lil.
Southwest: about the same.
Alaska: growth is slowing, but probably 5-8.
At the Nationals (jetBlue, Frontier, AirTran), you're looking at 2-5 years, depending on the economy. ATA is a big ? right now while they're figuring out finances.
Hope this helps.