Question to theists: When to take the bible literally?

[T.J.]

I thought this would make a good discussion in its own thread. Question to any bible-believing theist out there, but how do you know when to take the bible literally, or metaphorically? For example in the story of creation the bible says God created the Earth in six days and rested on the seventh. Some tend to believe this means a literal six days, others think it means there was a thousand or some odd years in a single 'day' because days to God are different from mortals. How did people come to this conclusion? How do you know when the bible is being literal and when it's being metaphorical?

Discuss.