I'm sorry to bring a negative post into it, but no-one ever said anything to me and I really wish they had now!
Just make sure that you don't set your expectations of the results too high, or at least make sure with your orthodontist and surgeon every step of the way that you realistically know what is going to change! It's easy when you are already self-conscious about your jaw/smile, and you are having lots of work done on it, to expect big changes. But really the results can be quite subtle, and may not change a lot. I became so focussed on my jaw and op that I convinced myself there would be a whole new me at the end of it! But there wasn't and two years on my confidence is lower than ever and i've needed therapy to help me come to terms with the whole thing. Not saying I regret having the surgery, I don't have an underbite anymore which can only be a good thing- I was just expecting more and just wish I hadn't gotten my hopes up so high beforehand!
Obviously this isn't the case for everybody, just something to bear in mind!