All of what's said here is true, but let me shed some light on how Porsche themselves do it (maybe someone that works at one of the training grounds PEC LA, PEC Atlanta, Porsche Driving Experience Alabama, etc.. can verify): to my knowledge, Porsche breaks in their cars for 200 miles before full track use at any of the experience centers here in the US. I imagine it would be the same for other countries as well. Those cars they use for track since new, are then sold to the general public, sometimes even as CPO cars. That's how much Porsche trusts their cars to be 100% road worthy even after being tracked and used for practice. That says a lot about the abuse these cars are designed to handle. This should ease the minds of potential Porsche owners before they decide to not buy a car because they believe it was tracked. Porsche sports cars are manufactured to a higher standard than that of their main competitors...
That being said, Porsche does "advise" a 2,000 mile break-In period before driving their cars aggressively. I believe this is the case of "do as I say, not as I do". =)