I just got a microsizer last night and even though I enjoy it it does have one annoying problem.
The motor runs at high and low speeds on it's own. I can be driving it and it will surge from top speed to half speed unpredictibly. I thought maybe the gears were binding but the motor surges even if the gears are off the car.
It is very annoying as it causes the car to spin out if it surges during turning.
Also the car gets about two minutes of runtime and then it really bogs down. Not close to the five or so minutes the other users have mentioned.
I run the car on flat tile and formica and it is completely stock with fresh AA alkalines in the radio. I also checked to make sure that the antenna isn't touching anything, and the car is very clean. I have about seven runs on it so far.