I carried my Canon digital camera in my hand for 39.3 miles! It didn't bother me at all- I just had to remember to move it to my opposite hand at waterstops. It survived just fine, and I've taken it on every race since then.
I totally understand wanting to run to the best of your abilities because you've been working hard to see exactly what your best is,

but I'd save that best run for another time and place.
The camera guys are in various places. Here's what I remember:
1) wandering around before the start;
2) the Castle (as you are exiting);
3) the open road somewhere (you'll see the mats and they're on some sort of tower contraption);
4) that Concourse from Epcot towards the countries- my picture has Spaceship Earth in the background;
5) the finish line.
There are probably other spots.
As for characters, last year I took pictures of/with:
1) Chip and Dale in Tomorrowland;
2) Alice by Tea cups;
3) Piglet by Pooh ride;
4) Ariel (on top of balcony of Castle);
5) Pirates- on a float backstage;
6) Penguins from Mary Poppins on the road by the hotels
7) Chip/Dale/Pluto- sort of vaguely remember- at finish line
And of course there are a bunch at the end.
Jen in GA