In fact, it took three attempts. The first was at Goodwood, which is a large flat open 3.8km (ish) circuit with an airfield in the middle of it: 11 laps in a time very slightly over 2 hours. The second I managed only about two thirds of, and the third - ah, Berlin.
If you do only one marathon in 2006, it should be Berlin. The course is a single loop of the city on lovely smooth wide proper roads (which have been closed for the duration), with 10000 or so participants and lined with spectators But, once you've done it you'll be wanting to do another, and as it's more or less the last marathon of the season, you're stuck.