The grade-skip we did for my dd was the best thing for her. (She skipped 1st and is in 9th now, so we've had awhile to see the results.) And don't worry about "socialization." It's easier to make friends with kids who are your mental age rather than merely your chronological age.
Its not simply a matter of being able to make friends, but instead being put into situations that require emotional precociousness. Or facing premature sexual pressure or expectations. These things are important considerations I think (I know!). I have to ask...have any of you experienced grade acceleration personally? Meaning you, yourself and you and not your children, nieces or neighbor's kids? Because I don't think all the ramifications are going to be apparent as they happen, or at least not fully interpretable by the accelerated child (who is probably going to believe that they are ready for everything before they really are) at the time.
I resent the implication that I can't tell whether or not my dd is happy with her grade skip. I've asked her, and I watch her level of happiness. (But if she were an unhappy child, that could be due to a whole host of reasons completely unrelated to the skip.)
Again, she's in 9th grade, and yes, she's experienced four years of middle school/jr. high, so I'm completely aware of how the whole "social" thing is going for her.
I also know what a miserable child she was in K, and how much she perked up in 2nd. So don't tell me it's not working for my child.
I'm not saying it's for every kid, obviously. (My son didn't skip.) But I'm trying to give the OP my dd's experience. It is working for her. (and throwing in the whole "neighbor's kid" thing is a straw-man argument. Obviously I wouldn't have the same knowledge of a neighbor's kid that I have of my own child.)