I have a 7 year gap, wasn't exactly the plan, we lost a couple in-between, but its how it worked out in end, I have nothing but positives for this, at times it felt like I had two only children, as at very different stages of their life-but they were rare occasions, eg one in nursery when one in primary, got younger into primary and sibling went to secondary after one year, now younger leaving primary while other in uni, it has meant though we have always been able to focus on child that needed it eg exams, medical issues etc different bedtimes and routines meant lots of time with us, in my case younger didn't sleep as a baby- or well really as a child still, so the older one went to bed earlier, as we knew this may cause problems we built special routines around this it was mum time while dh dealt with the terror!!
It has meant I will never have 2 teens at same time! and the bond between my two is so tight, by time younger was old enough to be annoying, sibling was old enough to understand. In fact at times they have confided in each other rather than tell a parent. I have had a great babysitter for last few years, there has never been any issues sharing clothes or toys or computers or net flicks account, as well grown out of , or use at different times.
Only negative is perhaps the little fellow got babied a bit as there were three people to run about after him and look after him.