The tread of the tires have a certain wear pattern if you have bad toe. It's called feathering. Like they mentioned, the tire kinda drags while it rotates. If there's evident feathering, then that's a definite sign that your toe is the problem.

I don't do burnouts and stuff like that, but I go through rears pretty quickly, too. They last longer than 5k, but if it's wearing normally, it may be just your driving habits, too =)