I also have been working with my dd to get her to sleep better at night. I have to have her completely weaned by early Dec (due to some medication I need to start taking soon). I haven't been having quite as hard a time as some of you, but it's been quite a process.
I started about 2 months ago when I was still nursing her to sleep, then night-nursing probably 4-5 times, and the again in the morning. (BTW, dd is 20 months old, so my experience may not be helpful for you parents with younger kids). The first phase was the longest (and really isn't completed yet), where I tried to get her to fall asleep without nursing. While she will go to sleep now, it will take her an hour sometimes to go down, and I often have to walk or rock her to sleep. Just 3 nights ago, I decided I could handle cutting off the tap at night. The first night was the hardest, since dd woke up every 2 hours or so demanding to nurse. My dh had a wonderful idea to give her a sippy cup with some water, just so she'd have the sensation of drinking something, as well as to put a little something in her tummy. It worked most of the time! Men do know something! :LOL Anyway, we've been up a lot the last few nights, but it's been getting easier and easier every night, until hopefully we can stop nursing altogether and get some sleep too.
As to the all night nursing marathons, I have a suggestion for that as well. At about 12 mo. I started taking my dd to a chiropractor who specializes in pregnancy and pediatrics. The way this need to suck was explained to me is that as the cranial bones shift in a growing baby's head, sometimes they get jammed. Specifially the bones related to the ears will cause a baby to want to suck to relieve that pressure, kind of a natural way to move those bones and uncram them. My chiropractor did some cranial-sacral (sp?) work on my daughter and that issue was a lot better for us. She still nursed several times a night, but not for an hour at a time anymore, and never for the entire night like before. One way to tell if this might be an issue for your child is if you can see a flat spot on their head, or if they pull on their ears a lot (almost as if they have an ear infection but without the screaming pain). If this is something you are interested in pursuing, let me know and I can try to get my chiro to log on and give you more detailed info.
Good luck to all of you! When it gets really hard, try to remember, this too will pass!