I know this is an old thread but its seems to be getting fired up again and since its one of the first ones that comes up when you google the topic I figured I would add my two cents. Prior to my first marathon(last week) I was a fair weather runner that got in at MOST 20 miles a week on average. Though lately, since its been cold, probably only averaged around 10-15 miles a week. Knowing that the marathon was coming up I ran 10 miles about two months ago, did about 9 miles two weeks before the marathon and squeezed in 14 miles exactly one week before the marathon. Most of my weekly mileage recently has been on a treadmill. I realize that this is not "running a marathon on NO training" but it is definately a long way from the conventionally recommended mileage. I had run my first half-marathon earlier in year the but, aside from that, my longest run EVER was the 14 miler one week prior to my marathon. I am a relatively fit 28 year old male about 140lbs with around a 22:00 5k PR.
The marathon was definately easier than I had expected and it is my opinion that anyone who can run a 5k in under 25 minutes should be able to complete a marathon in under 5 hours with very little training. I finished in 4:31 with all of my miles between a 10:00 and 10:30min/mile pace with very little walking and a couple bathroom breaks. I typically eat primal but began carb loading 3 days before the marathon and ate 4 energy gels during it. I had NO issues with cramping and very little muscle fatigue during the marthon however it is an understatement to say that my feet HURT VERY BAD. I wear Fivefingers solely when running and I'm sure that thicker soled shoes would have helped my feet but I think would have hurt my knees/hips/muscles worse. After about mile 16 I may as well have been running barefoot on sharp loose gravel because thats what it felt like. I realized about mile 20 that the pain was not going to get any worse and so I just endured it through the rest of the race. My legs were very sore after the race but no more so than my friends who had put in a good bit more training mileage than me. I'd say the soreness was on a scale of about 7-8 with 10 being the worst it could possibly be. It took about 4 days for the soreness to go away completely. There was some numbness on the inside of the second toe of my left foot that is still lingering after a week but otherwise I'm pretty much back to pre-race condition. I'm not real sure why I just typed out that whole experience but I guess its so anyone who is in a similar circumstance can take comfort in knowing that while a marathon on NO training might be pretty tough, a marathon on VERY LITTLE training is not so bad. I plan to run another one in a couple months, hopefully with a little more training ;)