Our kids are 26 months apart. Originally we were thinking more like 5 years, since I have a few friends doing it this way and it seems to work for them.... but then I lost my job and was unemployed last year, so we decided to do the whole pregnancy thing without having to deal with maternity leave, working etc. My husband kind of wanted it this way anyway so we could get all the baby-having done while all the gear was still around, and then move on.
So far my older one LOVES LOVES LOVES her younger sister, to the point that it can be overwhelming for her younger sister. If my older one is near a tartrum, often if we just bring the little one in the room it diffuses the escalation. It is hard work with such little girls right now, but I hope it will pay off with them being close as they get older.... time will tell.