"Flip flopping" is simply a derogatory term used as a talking point for the media.  Truth be told, situations change, that is the nature of the world.  I respect someone more if they look at new things that arise and say "Well I guess I've gotta look at this/do things differently now."  Had the Bush administration not been so stubborn, we probably wouldn't be in the mess we are today with Iraq.

Is it changing your opinion based on new information or is it changing your opinion based on the ebb and flow of public opinion?

There is a difference between just being stubborn and having the courage to defend an unpopular position because you know it's the right thing to do.