I'm not in Tae Kwon Do anymore due to financial/time constraints (although I'd like to start again in the future), but I was in it for two years and made it to the level of Brown Belt. I loved it!
I wouldn't have too much trouble with forms, kicking, punching, and sparring, but I had trouble with the two and three step techniques and hapkido holds, which make you use the concepts of left and right a lot, which I have a lot of trouble with. Also, I'd have difficulty imitating my instructors. They were really patient and understanding though, and always willing to help until I got it. It did make me calmer and more confident. When I had a bad day, I would really look forward to class. Once when we did meditations, I almost cried because all of the tension from the day was being released. I was also really amazed and proud at what I could get my body to do. It helped me focus better and want to be more self-disciplined too. I've always been a pretty peaceful person, but I would say it can definately make you feel more peaceful, because of it's calming effect and confidence boost, and because non-violence, self-control and respect for others is such a huge part of what it teaches-it makes you look at aggressive violence in a new way-as being wrong and cowardly. I'd definately recommend martial arts to other aspies-it might get a little frustrating at times if you have motor/coordination difficulties, but it's definately worth it.