It should be pointed out that if one is flying a lot domestically in the US on Delta, these flights barely help to advance your status in Flying Blue. Even transcontinental flights are merely "domestic" and so only earn 2XP in Economy, or 6XP in "First"...as mlin32 said.

I know that Delta has been making it progressively harder/more expensive to earn status in their own programme, but if you're a US based traveller who rarely ventures outside of the US, then whatever about the FB miles you earn and the utility you find in them, earning status is comparatively much harder than for an FB member based pretty much anywhere else in the world.