Cheaters
Is it worth the time to investigate and disqualify cheaters in races?
Yes!
Cheaters rob legitimate winners of awards and make a mockery of your event. These pathetic people should not be recognized for phony achievements.
Don't worry about making someone angry by accusing them of cheating. If you use chip timing, you should place pads at the start, finish, and farthest reach of the course. Anybody who did not cross all three pads evidently did not run the entire course.
The first time a cheater shows up, compare the finishing time to previous races. It may reveal a difference that cannot be accounted for by training.
Cheaters are not usually one-time wonders. Their bogus competition becomes a habit - at least until they are caught. Running clubs whose members are denied awards may want to assign a runner to shadow the cheater to catch him/her in the act.
If you disqualify a runner, post corrected results and send a copy to Road Running Information Center, where records are kept. If you don't do that, the phony time will stand and the runner may actually win a national ranking (this has happened).
Don't ignore cheaters. Cheating is serious and race directors should be prepared to stop it. See what Scott Hubbard says about this in Michigan Runner (p. 14, July/August 2008 issue).