well I have....
22mths between DD1 and DD2
34mths between DD2 and DD3
17mths between DD3 and DS1
26mths between DS1 and DS2
best gap for me was between DD2 and DD3, so I fell for DD3 just about on DD2's birthday!
best gap for them all to play was the shortest ones, as DD1 and DD2 are like twins at times (when not too hormonal), and then again DD3 and DS1 are also very very close.
DS2 tends to be close to only me+(I love him really), and so I wish hugely that I hadn't been so poorly having him that we felt unable (literally almost lost me and him...I had to be rescusistated at one point), to go for no.6...sooooo wish I had no.6!!
anyhoo.....now got 12yr,10yr,7yr,6yr and 4yr olds and they all (most of the time), play wonderfully together.
and if one has annoyed, there is always another playmate. for me that is a huge reason for going for them close....they (In my experience) get on better the closer they are. Does make it hard work as a mum, but as they get older and so get more independant, it reaps the benefits.