We do a Fartlek every Tuesday at work - not sure how good it is for marathon training but anything that gets your legs used to running faster must be a good thing...? I would have done more but for various reasons I missed a few. I am a member at MKAC but tend more to run with mates at work which is basically a support group!
I used a sub4 programme I found online & adapted it but basically week consisted of a LSR, x1 tempo, fartlek or interval session, x2 5/6 miles & a longish one in the week peaking at ten the week I did my first 20.
This year I concentrated a lot on core work in my training & also my diet (including really carb loading the week before). I also listened to my body & didn't run when feeling a bit rough. I also didn't run after the wednesday before the race & although feeling a bit tired I couldn't believe the difference to Brighton when I hit the wall. Anyway, smashed my PB & ran 3.58 & felt tip-top!
Lastly, I really enjoyed using this forum for all the tips, advice etc. But what I've really learnt is that we are all different & no plan is the same...