Spiegel has an interview with Murakami and it is thankfully in English:
Personally, I hope he has more than just four or five novels left in him. Read the rest of the interview to find out about his "unofficial" marathon in Greece, his best running time so far, and what running has to do with his writing.
SPIEGEL: Mr. Murakami, which is tougher: writing a novel, or running a marathon?
Murakami: Writing is fun -- at least mostly. I write for four hours every day. After that I go running. As a rule, 10 kilometers (6.2 miles). That's easy to manage. But running 42.195 kilometers (26 miles) all at once is tough; however it's a toughness I seek out. It is an inevitable torment which I deliberately take upon myself. For me that is the most important aspect of running a marathon.
SPIEGEL: And which is nicer: completing a book or crossing the finishing line of a marathon?
Murakami: Putting the final full stop at the end of a story is like giving birth to a child, an incomparable moment. A fortunate author can write maybe twelve novels in his lifetime. I don't know how many good books I still have in me; I hope there are another four or five. When I am running I don't feel that kind of limit. I publish a thick novel every four years, but I run a 10-kilometer race, a half-marathon and a marathon every year. I have run 27 marathon races so far, the last was in January, and numbers 28, 29 and 30 will follow quite naturally.
Can't wait for the book! (But then again I say that about all his books because I am such a shameless fanboy!)