I guess there are two:
Meeting the legendary roseabi . It's kind of weird to meet up three years after I bounced out of C25K into the Marathon forum so that I could take part in a speed challenge. Great to meet up though!
The other highlight for me was the finish: with about 200m to go, I put in some extra effort. Then someone sprinted past me. I wasn't going to take that so, with about 50m to go, I went for an all out sprint! Managed to overtake the guy (with some encouragement from him). So, a flat out sprint finish! Must have made an impression because someone from the crowd complemented me on my finish a few minutes later.