Massive thanks to all of you for your support.
I completed the marathon in 3 hours and 49 minutes, a time I'm very happy with as I was gunning for under four hours.
The first 30k wasn't bad at all, but the last 10k was a bit of an ordeal. Having ignored the advice to start off slow for the first 10k, I soon found myself leaving the 4.00 hour hare (a guy who keeps pace for a specific time and carries a flag with that time on it) behind and catching up with the 3.45 hares. I stayed in the 3.45 zone from 10k to about 30k, and even felt cocky enough to think I might be able to get into the 3.30 zone, but by 30k (about 18 miles) I realised I was overstretching myself. The 3.45 hares became shrinking dots on the horizon as I felt exhaustion setting into my legs, and from then on it was a mental rather than physical challenge. I knew it was best just to focus on finishing, knowing I'd make under 4 hours as long as I didn't walk.
It is a beautiful course with some stunning views of Paris, and the weather was bright and sunny. The crowds and atmosphere were great. My only gripe would be that at times the course narrowed too much, causing bottlenecks that once or twice forced everyone to slow to walking pace.
Immediately after the race we stuffed our faces in McDonalds, and later on went all out in a proper restaurant - snails, steaks, cheese plates, the lot - not to mention a steady supply of beer and wine. All in all a fine weekend, and I am wearing my limp like a badge of honour.
Thanks again to all of you.