Amy discusses the net value of a second income on page 24 of The Complete Tightwad Gazette. She makes some good points, and though the book is dated I still feel that it applies under most circumstances.
In particular, when childcare needs to be paid out of pocket, along with the costs involved with a second car and clothing for work, it is likely cheaper for one parent to stay home. Especially in this economy.
Be aware that I am a childcare provider. Saying this is going against my job. It is true, though.
What are your thoughts on this?