checkerboard biomes with extreme hills and extreme hills edge. Apatite for DAYS.This is why I've been using Steve's Carts for farming, so I can save my fertilizer for use in fermenters for biomass production.
Then again, I'm still playing on a world generated before the Forestry update, so I don't have a whole lot of apatite. I suppose I could create a Mystcraft Age filled with mountains if I ever start running low.