I'm definitely a pantser, at least when it comes to the first few chapters of a new book. I need to write a little way in to get my head around the characters, who they are, what they want and where they're headed. This can mean that I sometimes need to go back and re-write or edit, but then I don't think this is much different than time spent on planning writing character outlines/profiles, etc.
I do end up doing a little plotting as the book progresses, in that I start seeing the direction we're headed and what's going to need to happen in order to get us there. I don't have a structured approach to this, it's just something that seems to happen - lucky for me!
The best thing though, is when I surprise myself - when something I wrote back in chapter 2 suddenly becomes vitally important in chapter 11. It's both awesome and a little scary - I love that my brain works in ways I'm not even conscious of, although I do worry about what else might be going on in there that I don't know about!
I'll tell you more about the new story as I get my head around it...