My daughter (who is now 20) and my 3rd child (who is going to be 14 in 3 weeks) are 6 years apart. (Then there is an older brother who is 22)...so 8 years apart as well.
They did GREAT when I had my son. They played big brother and big sister to him to the fullest. Always kept an eye out on him and played with him. It was great. We never had any issues and now that they are older...my 13 year old does EVERYTHING with his brother. They are VERY close.
Now I just had a baby in April (who is 5 months old) and she is the love of my 2 older childrens life. Couldn't ask for better brother and sisters.
Sakari at 1 month old:
Sakari at 2 months old
2 months old
My children are 18/11/3 and one due in June I do like the space between....it was particulary good with 2/3 who are very close.