By the time a student graduates high school, he or she has effectively had somewhere between 50-100 different adult supervisors, learned to work in groups, learned the importance of deadlines, had to follow rules outside of their parents, and met a variety of people. I'm sure there are plenty of home-schooled individuals out there with a high IQ, making big bucks. However, I also believe there is probably a large percentage of them who have social problems because of their lack of "social experience".
There is also another group I'd like to bring into this and I'll refer to them as "testers". Testers are students who turn in very few homework assignments, but still pass the class due to their ability to soak in knowledge without homework support by scoring high on tests. In a way, testers are a hybrid of unschooling and class room students, because they spend their extra time doing something they "love", rather than doing pages and pages of math problems. I know quite a few "testers", especially in the IT/CS field because they were so addicted to their computers at a young age.