In the various news stories on the upcoming encyclical, it has been noted that a good portion of it was composed for John Paul II. The completion of it, as with so much else (the discourses on the Psalms last summer, etc.), fell to Benedict XVI.
After I read about Deus Caritas Est being partly John Paul's work, I had this funny little fantasy where each pope would leave unfinished business and that due to a succession of short pontificates, there would be this backlog of work that each new pope would pick up on, leaving less and less original work before the start of a new pontificate...
Now there is a post by Catholic Outsider on a proposed encyclical on charity that was not begun before John Paul II died.
I just hope that the Holy Father doesn't feel too obligated to pick up every loose strand left from John Paul.