Photographing London Marathon?

Hi has anyone any experience of photgraphing the London marathon?

If so can any one give any tips, advice re getting good images?

I will be going down with my wife on the first train to find a good spot about half way round so any advice would be really apreciated.

Have been on holiday for some time so need to catch up with whats been happening on the site.

Regards to all.

Trev