We are going through this at the moment with our almost three year old and it has been tough. We just transitioned him to the toddler bed.
I am new on this Web site so did not have the advantage of all this advice so I emailed my group of mommy friends and they listed a lot of what was on here: such as buy a gate, do the Snanny method, buy cool sheets, all with the excpetion of the gate I did.
My expereince: it has taken six weeks so far and definitely getting better, but it wasn't an immidiate fix like they show on the Snanny, at least not with my son.
I also, noticed that my son was struggling with falling asleep for some reason (this didn't seem to be a problem in his crib) so I started giving him suggestions--like try singing, try talking to your thomas friends. Then, I remembered this Worm that was given as a gift to my baby, and it plays songs, so I gave that to him, and that has really been helping.
I also, transitioned the separation, so I started out sitting in his room on his chair, then moved to the doorway of his room, then to the doorway fo my room, and now I am able to be in my bedroom. I work, so I made the transitions on the weekend, as each time caused him to get up several times again (in other words, each stage away from him makes him get up again--thus I wish I would have just went downstairs after the doorway thing--but that is next)
Part of our problem was that he would scream so loud that he would wake up his baby sister so then we would get to deal with two kids awake--fun, fun! So, I tried to do the right thing and keep his screaming to a minimal.
I was really, really frustrated thinking I saw this technique on the Snanny, why is it taking so long, but I suppose with some kids its dif.
he also still gets up during hte night, and we just put him back to bed, sometimes this works the first time and sometimes it takes two hours. So, who knows, maybe i will get to sleep through the nigh again one day.