Outlining or no?

When you're writing, do you outline your story or do you just sit down and start writing? I've never done much with outlining actually, but recently K.M. Weiland, who wrote a couple great books that I read a couple of years ago wrote another book, this one about outlining. As a matter of fact, the book is coming out today! In honor of the event, K. M. Weiland is having a grand giveaway over on her blog including a Kindle and a large selection of writing books!!!! So... in case you didn't catch the hint, you should really head over and check it out. ;)