I had trouble with two of my kids, and no problem with one. The first time we had trouble it was nipple confusion issues because of too-early bottle supplementing, which we did because my milk was slow to come in and the doc got on our case about not enough wet diapers.
The second time I had trouble was with one of my twins, who was low birthweight, had a weak suck, bad jaundice, and who lost far too much weight (about 20% of birthweight). She needed help learning to suck efficiently and help staying awake long enough to fill her tummy, and I needed help maintaining supply while she learned. Then she got hooked on the SNS and needed to wean from that.
DS latched beautifully, has always nursed like a champ, and has had no problems except just recently a case of thrush, which is really not turning out to be a big deal for us since he's not bothered by it and I have no symptoms. Hopefully we'll have no trouble treating it and it will be gone soon.