The London Marathon team have put in place a "track a runner by text" service this year. The New York folks had this in 2006 and I'm delighted it's made it to London this year.
If you want to track a runner - any runner - text the word "run" to 83040 (it's a service run by Adidas) and they'll text you back a link (or, they will do - it's not quite working yet but they promise it will be in a few days). Still, text now so that they know you want to get the link when it is working.
If you want to track my progress, my running number is 22801
Once you've signed up, the service will text you when I cross each 5km point. I'm not sure if it will be the same as it was in NY, but the time you'll get sent is my "gun" time (i.e. how long after the starting pistol was fired did I cross that point), not my actual time (i.e. how long after I actually crossed the start line did I reach that point). But if you're on the route, you'll be able to figure out roughly where i am, using an average of 5m 15s to 5m 30s per km.
Hope to see you somewhere on the route.