This article on the Mototune USA website describes a somewhat controversial method of breaking in a new engine. The manuals for our engines always tell us to start out with heavy oil(16:1) and break it in easy. This idea is increasingly becoming mythical as many people seem to have better results breaking in an engine by using less oil and using less oil. According to the writer, the most important period in the break-in period is the first 20 miles, and if it's not done right, the piston rings may not seal to their full potential. I'm assuming I understand this correctly.
Read more about breaking in a new engine "properly"!