No not really as long as you keep them dust free but just like any mechanical device they will wear out eventually.
If you fly in dusty environments then it will be worse and you can try to clean them out a bit but it will not help much if you keep on flying in dust. It will just shorted the expected life of the motor.
They are brushless motors and unlike the brushed type, will last if you take care of them. Check the temperature after each flight. You can buy a can of air to blow them out and cool them off.
I have been flying brushless since my helidays and have yet to burn one out. You can do it if you push them too hard. Like yufasa said its all about the environment. There are more sitting up crashed than with burnt motors.
While not required, it always helps to put a drop of high quality bearing oil on the upper and lower motor bearings about once per season. It helps them to run smoother, quieter, and generate less heat. While this is a topic that has been beaten to death in other forums, this is what I do. I have personally heard a difference in how quiet some motors are after this treatment - your mileage may vary.