Does anyone on Fluther have experience as a foster parent?

How does it all work? Do you need to make an open ended commitment? How long do most children stay with the foster parent/s? months? years? I know, of course, that it is nothing to be taken up lightly. I would imagine that the parents are carefully screened but what do they expect and require?
If you have had experience as a foster parent-was it good or bad?What would you say to someone who may be considering it? Assume this person has no children of their own that it would impact.