You won't go wrong with following the manual and what the factory or dealer tell you. There are two most important things in running-in and then operating the car for the future - 1) Correct oil level, 2) Carefully bringing the OIL temperature up to working temps

Besides that, there are about four different running-in procedures that people will list on this board:
1) By the book
2) Drive it like you stole it
3) Go easy first few hundreds of miles, then do what you want
4) Go easy first 1000 miles, then do what you want.

I did it by the book with strict adherence to the rules on warming up and then cooling down the car and my car performs fabulously. However, the engine kept on changing in character during each drive up to 8000 km. From then on it hasn't changed much, but it feels better and better. Today I have 14000 km and it is more explosive than for example at 10000 km.

2007 GT3.