The London Marathon is world famous and needs very little introduction; The 26.2 mile course snakes around famous and beautiful parts of Central and East London, thousands run and millions watch! My sister is running tomorrow for Great Ormond Street Hospital so I wish her, and everyone else, the best of luck. The great thing about it is that so much money is raised, the majority of people run for charity. One day I'm sure I'll persuade myself to do it; my Great North Run Half Marathon this September will be a good start (also for Great Ormond Street Hospital).
I'm not sure if people actually enjoy the 3,4,5 hours they're running the marathon for but the feeling afterwards must be incredible - I'll have to ask my sister afterwards! I'll be there watching, definitely the position I'd rather in given present fitness levels, but I'll be sure to get lots of pictures to put up on here.
If you're running tomorrow then Good luck! Raise lots of money, run a good time and enjoy it as much as possible!