I agree w/ShyRem on plan of attack, but let me opine a bit as usual.
In my head, applying for '09 means your app is ready in June '08. Your MCAT score is in hand, your letters of recommendation are either done or in process, your personal statement is reviewed and makes the sale. Your GPA is solid. Your list of schools is fine-tuned. Your schedule for completing prereqs is clear and reasonable. That to me is readiness.
Not being ready in June isn't a disaster, but June really ought to be the goal. And if you can't have everything tidy by, say, mid-August, then waiting another year makes sense. Part of this is risk assessment - if you plan to be tidy by mid-August, things can/will slip to September and then October and then you've wasted a great deal of money on a sliver of opportunity.
So let's talk about that MCAT. Fundamentally, can you do well on this test halfway through your prereqs? You need to take the test in April or May of '08 in order to apply in June '08. Is that feasible?
I think you're set up to do well on the bio/ochem (BS) section of the MCAT by spring, so let's not worry about that. I'm worried about your chem & physics (PS) readiness. Have you seen these subjects before? If you will be reviewing this material during MCAT prep for spring '08, that's a safe bet. If you haven't seen physics before, and/or you haven't seen the kinetics & thermodynamics in gen-chem before, that's not good at all. Personally I got A's in these subjects and still found the PS section to be very difficult.
I recommend that you take a practice MCAT right away. Before the end of the year, at least. I think the VR score is a key indicator, prior to beginning test prep in earnest, of whether the test should be taken within the year or not. If your VR is strong, then you're in a reasonable position to get a strong BS/PS - all the sections are heavy on critical thinking. For me, a VR of 10 or higher is a green light. More to the point, once you've taken a practice test, the MCAT loses its mystery. You can take a real test, for free, on
www.e-mcat.com.
To sum up, I think the decision point for applying in '08 vs. '09 is your degree of PS section readiness by spring '08. If you're not ready to rock this section in April, but you will be by June, ok. But if it'll be August, that's not a good plan.
Hope this helps. Keep us posted.