L.S.
You've got a lot of great responses, hopefully this helps too. I read that 3 years is the ideal spacing for children (and it's better to be a few months over 3 years than under). It gives the older child time to establish his/her own identity.
That being said, I have 3 girls. There is 3 years 3 months between my first two (and yes, when my first daughter was about 2-1/2 years, it hit me like a ton of bricks that I wanted another baby ... NOW!) I got pregnant with #2 right way and was on cloud nine. I was happier than I have ever been in my life when she was born. The age difference was ideal ... I was able to spend alone time with each of them because of naps and preschool. My older daughter loved being a little helper and life was wonderful. So wonderful in fact, that I got pregnant unexpectedly with #3 when #2 was only 9 months old. I hadn't even thought about having another child, so the news weighed heavy on my mind for many weeks. When baby #3 was born, I instantly fell in love, but also felt really really guilty because I was not able to spend as much time with #2, who was really still just a baby herself.
Fast forward ... baby #3 is now 16 months old and absolutely loves both her sisters. They all play together (and fight together too!) #2 however is a very difficult and sensitive child, and I know it's because she had to grow up so fast. It was, and continues to be very challenging to meet the needs of two very young children so close in age.
I really think it depends on the kind of person you are ... I think relaxed, laid back people are able to better handle multiple children close in age. For me, I know I would have done better if there were more space between my last two, however, I wouldn't trade my "baby" for the world!