Seems like there are about as many opinions on how much WorldBuilding is needed as there are writers.
I wrote a book for NaNoWriMo in 2009 with just a vague idea of my story world. It was fun but I still have to go back to the book, edit it and do some re-writing to make it anywhere near publishable. I guess I'm more the 'have to have a bit of things worked out ahead of time' sort. That is somewhere between the extremes of 'no idea where I am and just start writing' and the "I have to have everything major nailed down before I put pen to paper"types.