I firmly believed for a while that if the Bible said the world was made in 6 days then it was - no argument. But now, two things lead me to think this is not so;
a) As an earlier poster said, Genesis 1+2 were not written to be taken literally. William Barclay (theologian) points out that Hebrew people thought in pictures, not in reasoned and scientific arguments. Genesis 1 explains
why the world was created, because God wanted it to be; it doesn't actually say
how, this was not its purpose. The writer wanted people to know that the world is in God's hands, he made it, he controls it.
b) I believe that if the earth were only a few thousand years old, and rocks etc were created instantly and fully formed, there would be evidence that pointed to this. Scientists would make discoveries that confirmed what the Bible stated years ago. I am not in the least bit scientific, and cannot argue from this perspective. But I have been on the BBC science message boards where people who were qualified and held degrees in science, astronomy, geology etc were absolutely demolishing arguments put forward by creationists and the AoG website. How would this be possible if YE -ism was true? Why would God create the world in a certain number of days, and then allow people to find evidence and make discoveries that stated the opposite?
The answers given by creationists to these questions were usually along the lines of the fossils etc being "planted" as a test to our faith.

I do not understand why they think God would do that. Besides, I'm sure there are many scientists who are also Christians.
So my current view is summed up in my profile - God created, I don't know how or how long it took him. If I really need to know, I'm sure I'll be told one day.