We tried nightweaning (ala Jay Gordon) at 14, 18, and 20 months. At none of these points did it work. DS was up for 2 hours at each waking, and would last only 1 hour asleep each time. He was crying much of the time (in our arms, but still, it was intense). We gave up each of these times because we all were much better off with him nursing back down (pretty much every 2 hours). We started nightweaning again at 25 months, when I got pregnant, and it went much better. That time, he accepted it (protesting, but at least he settled within 30 mins). He would still wake between 3.30 and 5.30 and want to nurse, often for extended sessions. We decided to wait a bit on eliminating that one. At 29 months, we started on that one. We offered him milk and a snack, and he accepted that (a favorite snack). We've been doing that ever since (it's beena month). So, nightweaning did non work until 25 months. Even then, he still wakes up once. It's much more manageable, though! This is down from waking every 2 hours!!
I can't wait until my milk comes back in with DS2. If DS1 is still waking at that point, I'll be able to nurse him down again, and he'll lose less sleep (it takes him 30 mins to settle on his own with the milk and snack).
I remember wondering whether nightweaning would really stop the waking! I think you have to wait for the developmentally appropriate moment for your child. One of my friends was more successful with nightweaning earlier (but also left one feeding between 4.30 and 5.30 until a little after age 2), at around 18 months. But, he's 2.5 now and still wakes every 3 hours anyway. Another friend of mine's son was nightweaned at a year, and his sleeping varies a lot. He woke a lot looking for his pacifier. Some nights, 7 times in the night, others, zero. It really depends on your child and their readiness.