My kids are a year and a week apart. (*Yes, on purpose!). I love it, the oldest doesn't remember it just being her, so she always thinks of her brother and them together as a unit. Being pregnant the second time was great, the first still slept a lot and wasn't mobile, so I could rest easily. It was helpful to go through similar stages and interests, they always have someone to hang out with (they are 12 and 13 now).
*I was mid-thirties and didn't know how long it would take to get pregnant again so we decided to see what happened. DH worked at home and I had spent years working in infant daycare so wasn't worried about having 2 young ones so close.