I have just one kid who is about 2.5 yo. Honestly, I see moms with toddlers and babies and just don't know how they do it. It looks SO tiring to me!
We will probably wait till ds is about 4-5 to have another one. This gives us both time to finish school (I'm a grad student, dh is an undergrad), and hopefully we will be in a position where I can take the first year off work to care for the child.
Ds will be fully potty trained, hopefully be sleeping in his own bed all night (this is important to me because I love co-sleeping but do NOT want to do it with TWO kids), and will be old enough to amuse himself at times and possibly even amuse his younger sibling. He will also be old enough to understand that he needs to be gentle with the baby (a friend has two that are not quite 2 years apart and she says the older one will try to hurt the younger one when he is tired and it's really hard on her because she wants to protect her baby, but the older one is her baby too
Further, down the line....there will be a LARGE gap between when they can drive and go to college. This is important to me because I want to get my kids a car, but I don't think we could afford to have FOUR cars! Also, I would prefer to have just one kid in college at one time. I know that our money situation could change, but realistically, I don't think we'll ever be having tea with Mr. Monopoly and I want to retire with dignity and I ALSO want to be able to do the things for my kids that my parents didn't do for me, so thinking that far ahead helps me to be rational when I look at ds' itty bitty baby clothes (had to get them out for a friend).
I also have age on my side. I'm 27 now, so I will be about 30 when my next is born. If I were 37 now, I would be TTC right now. Further, because I'm only 27, even though I think I want just 2 kids, if I do decide I want a third I have time to do that.
Finally, I'm selfish. I really LOVE being able to go to yoga class, to occasionally go to movies, get a pizza, read a book, etc....all the things that require time and money. We don't have a ton of money right now, but we are able to do things like buy new running shoes or see Harry Potter because we only have one child. In our situation, if we had a second, we would literally not be able to do anything but care for those kids. Oh, and that reminds me that d/c is expensive, too, and having two kids in d/c at once is REALLY expensive but I want to WOH.
Just my .02!
Good luck with your decision!
Oh yeah: I adore this time with ds. I don't want to have to split my time between him and another dc. Although I haven't BTDT, I agree with the PP who said that it's hard on EVERYBODY to have kids so close together. I don't want my ds to have to wait for me to finish with his sibling for my attention. Not that if you choose to have two together you are a bad parent or anything....I think this comes back to my selfishness again. I want ds snuggles all to myself!