Doesn't porsche always make changes to their cars? Horse power bumps, minor body and suspension changes etc. From what I read I think MY 08 released in summer 07. If not then, I hope they hold off until the 998 model.
Look at this article about the 996 changes that occurred in 02. I would say significant changes. If the 997 follows in the same mold I think we are in for some great alterations.
http://www.roadandtrack.com/article.asp?section_id=6&article_id=77