We're kind of ...
As in we're not using contraception, but it's unlikely to be soon because dd 15 mths is still breastfeeding pretty enthusiastically, and we weren't able to conceive her until #1 decided to wean.
To answer your question, I think the nervousness is still there but a bit different. In some ways nothing can be as much of a shock as the first baby, but on the other hand I can now worry about finances, how the older children will cope and how the new child will alter the family dynamics. With pregnancy and birth, it's nice to think I'll be an old hand at it all, but then I wonder how I'll manage being older, more exhausted and out of shape.
Also you just don't have as much time to think about it do you? With TTC #1 we actually worked on it for a year beforehand, getting really fit and healthy. Then you have lots of time during pregnancy to wonder at the miracle of it all. With two young children there just isn't the time for navel gazing, as you would know.
BTW both of mine were WInter babies and I thought it was great. I wouldn't want to be 9 months pregnant in hot weather, and it was lovely to spend some babymoon time snuggled up in front of the fire. Also more convenient for dh to take leave when it's not the popular holiday season.