Jo, I hear ya! Love children to bits (especially the rugrats stage, strangely enough), but also LOVE LOVE LOVE the freedom to hand them over to their parents and head back to my nice, quiet, peaceful home :P
As of last month, I'm effectively sterile - and WAY relieved. Never wanted to have my own kids, decision made as an 18yo, and never the temptation to change it. My plan back then was I was only going to adopt, and if I was single at 30, I would simply adopt on my own. In addition to growing up and living in the real world now, and liking my freedom to do things my way, health issues also mean that I will not be approved for adoption AND I wouldn't want to take the chance of orphaning a child all over again either.