hey all,
just thought i'd chip in, since i was in exactly your position at this time last year (in the days before i had discovered sdn!). i decided in mid april (04) that i was going to apply for fall '05 matriculation. i had luckily taken all of my prerequisites, but it was obviously too late for the april mcat. basically i was told this. if you get your applications in EARLY (start working on those personal statements now so they're done by june, and request your transcripts soon too!), and you're fairly confident that you have the potential to do well, go for the august mcat. your application, if you get it in early (like, early to mid june) will be held anyway, waiting for your august mcat. you want to get it in as EARLY AS POSSIBLE, so that you can get your secondary AS EARLY AS POSSIBLE, which you will then submit with your fee AS EARLY AS POSSIBLE (sense a theme here?) so that basically the only thing missing will be your mcat scores. once they arrive in october, your application will be complete (don't be a ******* like me and forget to send your photo to columbia -- i got an email in the fall saying my application was incomplete because of this!) and will go promptly to the committee who will decide whether or not to invite you for an interview.
the other really big problem is that you only have one shot for this year. basically you'll already have spent at least $1000 (probably more like $2000 if you apply to lots of schools) in primary and secondary apps, which, if you really blow the mcat, will be wasted since you'll wind up having to do it again next year. this might be something you want to take into consideration.
now, about the mcat, i studied my butt off from april to august of last year (really killed my summer), worked with a study partner, took 9 practice tests, built up my stamina, and went in and scored a 32. so if you start in time, it's definitely possible.
so, you're all asking, does it hurt you to take the august? probably. it's a disadvantage, but not an insurmountable one if the rest of your application is strong. my friend had amazing grades, amazing recs, amazing non traditional story and got interviews and acceptances at a bunch of top schools with a really really really good august mcat. myself? i had a decent gpa, (though not stellar - you can see mdapplicants for my stats) fairly good mcat, what i thought were pretty good recs, and lots of really interesting extra currics and post-bac experiences (though not much clinical). out of 20 schools i only got 4 interview invites (one of which i declined) starting in december (when the april people start getting invites in september or thereabouts), one waitlist, and one acceptance. it's definitely frustrating when the april people are starting to get acceptances from the rolling schools and you haven't even gotten an interview invite yet! the first invites for the august people will probably come in late october or early november (since scores are released in mid october). yes, it's hard and the whole process is stressful and terrible. but work your butt off and you can do it. feel free to send any questions my way. good luck!!!
Anyway best of luck to everyone. Sometimes it is not when you get there, it is that you got there that matters.
As you can see from my post you are 3 weeks ahead of me. Any way, I myself know that I cannot wait until April to take this exam. That means another year of waiting. 
