Facebook says so
URL in the Developer Application."
So, what Facebook user data are you going to use? How will you use it?
I use your profile picture to show next to your username, your list of photo albums to allow you to choose from previous albums and your list of friends to allow you to easily tag people in your photos. I re-query all this data each time you use the application,
because I throw it away after you're done uploading photos.
Any other user data?
Any pictures that you hand to this application will be uploaded to Facebook, along with any captions you added in Windows Live Photo Gallery. Duh!
Overall, your data is safe and stays between just you and Facebook.