This was my second FLM; I last ran in 2003 in nearly identical conditions. The best moment for me was undoubtedly seeing my girlfriend and my family at miles 14 and 22. It gives you such a lift to know you've got your own personal fan club! Coming a close second had to be getting my Lucozade Sport handed to my by James Cracknell.
My worst moment was when I hit the wall at mile 18. I don't remember this so much last time as I was running with a friend but this time on my own it felt like the world and his wife were streaming past me. I was on for a 3:45 time but as my target was sub-4 (I did 4:10 last time) it wasn't the end of the world.
The most memorable moment for me was repeating the mantra RW suggested I have for the tough times "I am a good and strong runner and I can and will finish" through the last six miles.
The thing I would try to do differently I think would be to try to have a training partner for next time as it helps to have someone to spur you on. The key to my success, and it was a success as I did it in 3:52:29 a full 18 minutes faster than last time, is that when things get tough keep telling yourself that you are a great runner and that you will finish. The positive mental attitude works wonders.