Susie--I may be banished from the DIS forever for saying this, but I actually do not enjoy running LRs at Disney (other than the marathon, of course
).
It is difficult to find a route for a long run that does not involve tons of "laps," but even more than that, I do not enjoy running long runs on concrete. A lot of the running paths that Disney makes available for runners are concrete--as opposed to asphalt. Most of the roads are asphalt, but running alongsided the roads is discouraged (and dangerous). I have not done so, but I have read threads where people have been stopped along roadways by Disney security and asked to find a different course to run.
That being said, my favorite places to run at Disney are the paths between Fort Wilderness/Wilderness Lodge and the internal roads and paths at Saratoga Springs.
As im4disney said, the BW/Studios area is pretty cool, too, especially in the morning before the "World" wakes up. I have not run in Celebration, but I bet that would be good, too.
Steve
I can't think of a better place to be. 
