As requested, here's my (Mike) marathon training plan. Its only the last 12 weeks of an 18 week plan. I use this plan as a guideline mostly. Sometimes I'll do 2 tempo runs in a week. Sometimes I'll cut a run short or stretch one etc. At one point I got behind on my long runs so I limited my mid-week mileage so I wouldn't be increasing the overall mileage for the week by too much and possibly getting an over-use injury. I do try to make sure to always do what's prescribed for the long run.
I'm no expert and I wouldn't tell anyone else that what I'm doing is the best way to train for a marathon, but I'm pretty confident that I'll do pretty well come race day. I made that determination after my first 20 miler.