Wow, thats two completely opposite opinions. I'm a relative newb and this is how I broke in my engine and have had no problems with it:

I place the car on a stand and started it up. I let it idle for a tank, I then repeated this. After the second tank of idle. I placed it on the ground and did very slow (1/3 throttle max, not even that much) passes along a straight road, while adjusting steering trim. I repeated this a lot, gaining in confidence (and speed) over about 6 tanks. NOTE: This was my first real RC car so I was learning how to drive at the same time, I never went to full throttle at all through the whole break in perios, and still havn't really gone above 35mph. After my 6th tank, I took it to a big open car park and let all hell loose...