There was mention of new cars being made with synthetic oil in the crank case from the factory. IMO, there is a huge difference between a Corvette or Porsche versus a little 50cc engine. The machined tolerances should, in theory, be much closer in a high end vehicle as compared to a small inexpensive engine. In either case, I would change the oil very quickly in a small engine and switch to synthetic after a few hundred miles, if at all. In my cars, I wait 1,000 miles, change oil, and switch to synthetic.
This topic has been debated endlessly on about every forum. From what I've read on motocycle forums is that it's actually heat cycles that break an engine in - going from full cold to normal operating temparature and back again.
--John