The main arguments I would give for a non-literal interpretation are as follows:
1. Stylized text
The content is structured into six days, with parallelism occurring between the days. The first three days are composed of the creation of empty spaces; on the last three those spaces are filled. Day 1 corresponds to day 4, day 2 to 5, and day 3 to 6.
From “Making Sense of Genesis 1” by Rikki Watts:
“Turning first to the form, even a cursory reading of Genesis 1 reveals a great deal of repetition: “and God said” (vv. 3, 6, 9, 11, 14, 20, 24, 26, 28, 29), “let there be” (or some form thereof; vv. 3, 6, 9, 11, 14, 20, 24, 26), “and it was so” (vv. 3, 7, 9, 11, 15, 24, 30), “and God made” (or similar action; vv. 4, 7, 12, 16, 21, 25, 27), “and God saw that ‘x’ was good” (vv. 4, 10, 12, 18, 21, 25, 31), some form of naming or blessing (vv. 5, 8, 10, 22, 28), “there was evening and there was morning” (vv. 5, 8, 13, 19, 23, 31), and then a designation of the day as first, second, etc. (vv. 5, 8, 13, 19, 23, 31; 2.2), with most of these occurring seven times. ”
2. Mode of revelation
The simple fact that this is the only historical part of the Bible without any human witnesses. Either a) its content was revealed in a vision or similar or b) the content was a reshaping of other creation stories. Both options create problems for a literal interpretation.
3. Similar features to other ancient creation stories
4. Practical considerations
eg. day and night, light and darkness from day 1, when the sun and moon are not created until day 4. Where did the light come from?
Ultimately the best interpretations are either the literal one or an allegorical one. I agree with NewiQue that the days are clearly indicated as 24 hour days. Interpretations that try and squeeze eons of time into each of the days in order to allow for the theory of evolution stretch the text beyond all recognition.
I probably shouldn’t even have mentioned science in the previous post as it is a red herring as regards Genesis 1.
The Second Day 
I asked specifically in the last post why we should read Gen 1-2 this way and not, for example, Gen 17 — which is also very stylized literature.
If the creation account in Gen 1 is intended to point the reader to non-literal interpretation, why shouldn’t we seek a non-literal interpretation of Gen 17 and mythologize the covenant with Abraham?
“Practical considerations” don’t enter into it, btw. The “practical considerations” of a bodily resurrection from the dead for Jesus are -at least- as challenging as thinking of Creation happening in 6 days. The coda at the end of each creative action is “And there was evening and there was morning, the -X- day” — which has nothing to do with the rotation of the Earth, the position or existence of the sun, or any other phenomenological referent: it has to do with the closure of the measure of time. It’s rather odd to admit that the text is “stylized” and then ignore the force of the stylized features of the text.
I don’t see how Gen. 17 is stylized; not in the same way Gen.1 is anyway. To me, Gen. 17 reads as straight narrative and has no features that hint at anything other than a straightforward historical narrative. Am I missing something?
You noted in a previous comment that you are no fan of Answers in Genesis. I take it then that you do not agree with their interpretation. How do you interpret Genesis 1?
Point taken on practical considerations.
I agree with your critic Centurion that the stylisation of Gen.1 doesn’t prove it isn’t straight narrative history. Perhaps a better parallel would be the psalms e.g. Ps.136, which tells of creation in the same style as later history. Genesis in Space and Time (Francis Schaeffer) was helpful to me here. It proved (to me) that we can’t see Genesis 1-11 as just non-historical allegory or myth. On the other hand, Rikk Watts’ article introduces a new level of sophistication into the discussion.
You yourself seem a bit undecided. Do you incline to take Gen.1 literally or not?
I’d also like to add one other thought. We get caught here in what are often false alternatives.
Does Gen.1 have to be taken historically or mythically? Could it be both- real history in mythical language? (similar thought in other parts of the Bible, e.g. Job, parts of Revelation).
Is it a case of literal creationism or evolution? Maybe both are wrong, which I think is Watts’ position.
Are we afraid to debunk AIG creationism because it’s seen as that or theistic evolution or even liberalism? Again, maybe they’re all wrong.
For what it’s worth I would affirm:
1. Gen.1 tells real history, but not in a literal modern sense of that word.
2. Evolution is absurd as an explanation of the universe as a whole, especially the personhood of human beings.
3. A proper interpretation of Gen.1 means that we consider what the author wanted his readers to understand, in the context in which they read it. Now we can’t know this completely, but if we disregard it, we will end up with all sorts of loaded views that have more to do with our battles than the author of Genesis’.
Jon
You are right – I am undecided at the moment as to how to handle Genesis 1. Ideologically the young-earth creationist view does appeal to me, I admit. I swallowed an awful lot of their material, after all.
For now I’ll adhere rigidly to the fence-sitter approach, refusing to decide one way or the other.