Guys,
I've found an excellent article explaining the reasons for and the type of damage that occurs when you fail to pre-warm an aircraft engine or go to full throttle before it warms up sufficiently.
http://www.avweb.com/news/maint/182846-1.html
It's as much about bearing and piston clearances as the viscosity of the oil - which was new to me. Essentially, on a cold engine the clearances between the moving parts are much reduced (or almost zero sometimes) which means less space for oil to penetrate and more metal to metal contact causing bearing wear, spun bearings and piston scuffing etc. While there is a danger of engine seizure on the ground, far more dangerous is the potential for failure during or after takeoff due to the hidden damage caused on startup.
Interesting quote:
"In less than a minute, a single cold start without proper preheating can produce more wear on your piston aircraft engine than 500 hours of normal cruise operation. If it's cold enough, a single cold start can cause the catastrophic destruction of an engine shortly after takeoff. This is serious stuff, folks!"
Wouldn't it be great to see guys falling out of the sky or forced to operate under reduced power because they abused their precious powerplant?