I can attest to this a bit as I've known several people, and I'm sure I'll get blasted, but this is just my experience...
If you want your kids to be super smart and excel in academics but suck at making friends... send them.
If you want your kids to have decent social skills, and decent academics... send them to normal school.
If you want a decent balance, send them to montessori through like 3rd or 4th grade, then get them the crap out of there so they can learn to play with other kids.
Out of the people I have known that went to those, none have been totally normal.
One chick is super duper hot, OK but not great social skills, she's super smart, but she sits at home and reads all day, she's 25 years old, has no job, has no desire to get a driver's license, and she has a kid.
Others I've known are just odd, they don't know how to interact with people on a social level. Some kids were just spacey and wanted to sit and do their own thing not understanding how to play with the other children, and another guy I knew looked at me one day and said, "I wish I had a chance to be young again and make friends." He was like 20.
Some parents of a girl they were considering sending I brought up the social problem and they said, "Oh, don't worry, we know... 4th or 5th grade and we'll put them in a real school. We've seen the social issues."
Flame away