Porsche claims 4.6 sec for the 997S and 4.8 for the regular 997 and magazines have anyhing from 3.9 to 4.4. I was told by one of Porsche executives that Porsche's testing is very conservative as they drive their cars in a manner where an average driver should be capable of achieving the same results, meaning that a pro can eaily get better results. Check this out:

http://www.roadandtrack.com/article.asp?article_id=1949&section_id=31&page_number=8