We have 20mths between our first three, then there is a 3yr3mth gap between 3 and 4. It has worked out so well for us. I am loving having the gap like it is because now I have DS2 at home on his own for another 2 years before he starts school in 2013. It's hard to explain why it works for us, but it does. he just slots into things perfectly. Even with there being 6.5yrs between DS1 and DS2, they are still really close and spend a lot of time together, so I think if they are going to be close, then the age gap is irrelevant kwim? I wouldn't have had it any other way and think life would have been harder if we had them all close together.