At the point where I had ds3, I would have been paying all but £2 of my take home pay to the nursery. To be honest, this wouldn't have got any better once they went to school, as my hours meant they would have needed before and after school club, and that was viciously expensive.
Dh and I had always planned family finances on the basis of his salary alone - mine was added extras, not counted into the basics - so we knew I could stop work and the family finances would work - so I did.
I know it was the best decision for me and my dses. As it turns out, I was battling depression at that point, and things have got worse as I've got older - and I doubt I'd be employable now.
I have done things to contribute to the community - PTA, playschool committee, scouts committee, school governors, treasurer for an art club, residents association secretary. I was, and am also able to attend all the daytime stuff at the school without loads of hassle or having to take holiday. I don't envy WOHMs that stress. At the moment, I am concentrating on my recovery from depression (or at least, reaching a point where my mood is stable and reasonably peaceful, with occasional happiness).
On a practical point - where the hell are all these jobs that all the SAHMs are supposed to waltz into? Correct me if I am wrong, but I thought we had far more people seeking work than vacancies, at the moment (and that's without factoring in all the SAHMs who are happy to be so, and are not seeking jobs). I must have missed the news item about the creation of millions of jobs, and the dearth of candidates applying for said jobs. 
I think that most of us do what is right for our families and ourselves - but because we are not all identical, what is right for me and my family could be dead wrong for you and yours. I do hate all the comments that seek to portray one choice as superior to the other (like Xenia's remark earlier, or comments about WOHMs missing precious moments/why have babies and have others care for them).