My son's iPod Touch 4th gen. headphones jack didn't work.
Everything went (almost) smoothly, a bit nervous at the beginning (both my son and I) but I could relax enough to enjoy the challenge.
Be carefull on step 6 when you try to remove the copper cover. It is hold by a tiny piece of plastic snapped into a slot in the cover and can be easily broken (I broke it). Try to pry from well down the opposite side of the spring (where the plastic catch is located) to release the piece, it should spring open.
Don't use too much force, try to figure out how it was assembled and be relaxed.