We've discussed this pattern many times on here, and it scares me as well. But some have mentioned that part of that may be more about arrogance, pride, and preparation. Look at how things have gone for him...
He has a good season in 2003, is coming off a World Series high and declines a bit in 2004. He has a good year with Florida in 2005, is traded to Boston, and-- like most players-- takes a year to adjust to his new team.
He has a good year with Boston in 2007, declines a bit in 2008 after another World Series high.
In 2009, he has a good year, and falls of the cliff at the end of the year, and it drags into 2010, where he is injured.
In 2011, everyone is saying he is done, so he's motivated to have possibly the best year of his career.
Personally, I think he's a lazy sack of s*** that takes every other year off. I have disliked him as a player since 2009, but when he is working hard, and he is on, there are very few better pitchers. There is so much pressure on him after he fell apart in 2011 that I believe that he's going to be motivated to succeed in 2012.