Should we get an au pair?

Every week a Guardian Money reader submits a question, and it's up to you to help him or her out – a selection of the best answers will appear in next Saturday's paper. This week's question I have to return to work after the birth of our second child. Looking at child care costs, the cheapest solution seems to be an au pair. What will it be like to have another person living with us? How much should we pay? Will our leftie friends still talk to us? What are your thoughts?