I took the motor for my eGo apart the other day to inspect the brushes and commutator after gearing WAY up (40mph) and noticed something interesting:
I saw that while the motor itself has holes drilled into the end for exhausting hot air, when it is bolted to the jackshaft assembly, these holes are 99% blocked, forcing the airflow to turn 90 degrees in order to exit the motor. 
I also noticed that the other end of the motor, where cooling air is drawn into the motor, the inlets are on the side of the motor, allowing the air to bypass the brushes and commutator where cooling is needed most.
I'm thinking that these two things are working together to prevent efficient cooling to take place. I intend to drill holes both in the jackshaft assembly where you can see buildup of dust, and in the commutator end of the motor, maybe at an angle towards the center to help air move more freely, and to direct it at the hottest part of the motor.
