Let me give some serious advice to those of you wondering if you should retake or not. First off, the distribution of your score matters. No one will give half a $#!t if your score is a 31 if your breakdown is 12BS 4VR 15PS. An applicant with a 30 whose breakdown is 10BS 10VR and 10PS is considered much stronger.
Okay, that said, if you scored a 7 or lower in any one section, you should consider retaking. I know for a fact my file was tossed out of Wake Forest because I had an 8 in Verbal (I asked, and that's what they told me). It's BS, but the whole application process is BS. It truly is. It's the most arbitrary thing in the world; who knows if one more question could have swayed me to a 9, but whatever. #uck it. Don't bother asking yourself all the what-ifs, save yourself that misery and focus on goals instead.
Do not consider retaking because of the writing sample, unless you scored something truly dismal. Like a J, or a K, in which case you need to stop answering the prompts in Klingon or doodles. No one give's a rat's ass about the writing sample anyway. They pretend they do, but really they're all about number whoring.
So, now let's talk numbers. I would personally encourage someone with a 27 or less to retake, unless that 27 is distributed as 9/9/9, or even a 8/9/10. Again, totals are somewhat arbitrary, but if you have a 26 overall (or lower), you are NOT competitive in terms of your MCAT, and your GPA better be stinking high so that you could write-off the MCAT score as just a bad test day. Otherwise you'll get iced.
28-29 is the troublesome territory, for those of you considering a retake. I personally told myself, if I got a 30 or higher overall (with reasonable distribution, of course, and NO 7's or lower) that I would NOT retake. Of course, what do I wind up getting, but a 29 (10/8/11). I decided NOT to retake on that 29, because the distribution was alright (albeit the 8 was low enough to get me rejected) and I thought, "what the hell, why not test out the waters."
30's and higher: for chrissake, don't retake. 30 is a solid score. 29 is even a solid score. Do not get any inflated ideas in your head reading SDN. If you retake, and you go DOWN, it will hurt like a bitch. Emotionally, and on your file as well. Why put yourself through it? Be confident about yourself. Be confident about your score. You cannot go through the app. process feeling defeated, or you're doomed from the start. Wise-up. If you're in this category of people, you did FREAKING AWESOME and there are plenty of people who would die to get what you got. Be grateful, you little farts.
Again, just to sum up: (1.) don't get any inflated ideas in your head, 28-30 are solid scores despite what you read here on SDN and mdapps; and (2.) stop thinking of the scores in terms of the total. I know I've been talking about them in terms of totals, and that's okay to some extent, but seriously think about the breakdown. Treat each section like a separate test: if you got 7 or lower in any of them, that will be a problem. An 8 is low too, but not unforgivable. Double digits are GOLD. If you have three double digits, you did #ucking outstanding. Applaud yourself and apply with confidence, and don't even doubt it or think to yourself about retaking.
Alright and now as my final words, I have to throw in the obligatory "it's not all about the numbers" crap that some people like to believe. Well, if you got a LOW MCAT score, and by low I mean both in terms of total and distribution, a good GPA can redeem you. You will hear about people with 27 MCATs and 3.9 GPAs who get into many schools they apply to. I know there's been a lot of debate over these forums about which is more important: MCAT or GPA. The answer is "both", but GPA is very, very important too. It can certainly make up for the MCAT, and to some degree, the opposite can apply. EC's, volunteering, etc. are "important", but VERY important is exposure to the medical profession. You better damn well be able to explain why you want to be a doctor, and CONVINCE the adcom that you're right for it, and the only way to do that is to experience what you claim to be so committed to, build on that experience, and express your sincere and mature motivation and dedication to the medical field.
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By the way, for reference, with my 29R (11PS 8VR 10BS) I got 3 interviews, 1 acceptance, and I'm still on 2 stinking waitlists. I did get a slew of rejections too, but I have yet to be rejected from a place I interviewed at. All 3 interviews were allopathic schools.
J/k
with your apps. 
