Red Shirting - How do you weigh in?

I have read a thread on our Ethiopian adoption message board this past week regarding a topic I find very interesting. The topic was around red shirting your child (AKA having your child repeat preschool or kindergarten). On this thread many parents and parents who are teachers weighed in on this topic and brought up some interesting things.

Few things stood out to me:
• Boys tend to be "held back" more so than girls due to not be socially ready
• Appears to be a trend in many areas through the US
• Kids may be academically ready but not socially ready
• Kids may be ready academically and socially but once they hit middle or high school, they may have issues socially
• Parents of summer babies tend to have their child repeat a year of preschool before sending them to kindergarten as many parents on the forum felt is was better to be the oldest in the class versus the youngest
• Those who can afford another year of preschool tend to have their child repeat it and those who can not afford it, send their child to school

I guess there isn't a right or wrong opinion here. To me, I want to do the best for my children and what is best for them. Dave and I moved up Makenna's birthday two weeks and now she meets the cut-off to begin kindergarten at the age of 5. We of course did not move up her birthday for this reason. If we send her to kindergarten right when she turns 5, she will be the youngest in her class. I actually was thrilled to find out we met the cut-off date as it would mean one less year of daycare bills. Call me naive or uninformed but I really didn't think about whether Makenna would be ready socially or if it would be an issue when she is in middle or high school. My concern was academically. I guess I just assumed she would be ready.

How do you weigh in on this topic? I'd love to hear from other parents on this as it seems to be a hot topic out there and one that is creating a trend.