EDIT: Note to self, read up on the difference between 'sentience' and 'sapience.'
First, do you think we'll even be aware of our machines becoming sapient? Will we recognize this as 'life'? Will the transformation of machines into sapient/living beings be sudden, or does this kind of thing happen over a spectrum of shades of gray?
Second, how advanced does a thinking machine need to be for us to grant it personhood? How do you define personhood? My opinion is that humans are persons in the same way that a square is a rectangle.
Third, do you think machines will be capable of experiencing pain? What is pain if not a chemical reaction? Surely a sufficiently advanced program can simulate that? Will we need to intentionally program machines to feel pain, or will it happen spontaneously? Do you think what http://i.imgur.com/dXLb8.jpgwent through at the end of 2001 was painful/suffering? I felt like that scene is completely plausible.