In April, I saw the London marathon (more precisely, a tiny part of it) live on the Internet. The quality wasn't really anything to wax eloquent about. Nonetheless, for a runner deprived of live TV coverage, it was a blessing, especially given the field. At least, you could hear the commentary clearly.
It would be interesting to see if we could leverage the power of technology even further. Imagine a marathon (or any other race) website streaming the live coverage along with a list of the top N runners at any given time. You click on any name and it displays the current data for the runner - current heart rate, current pace, average pace, and other interesting statistics. Given the plethora of personal monitoring devices (e.g., heart rate monitors, etc.) that exists today and the availability of wireless networks, the task in itself shouldn't be too complicated. Of course, it would be up to the runner whether he/she chooses to have that data streamed. On the other hand, if everyone or even half of a field in one of the big ones such as London or Los Angeles decided to go for this, it could pose some interesting scalability problems for wireless delivery.