Vista - photo friendly
There's a great post over at the Microsoft Photography Blog which describes how Vista manages your photos - in particular how you make changes and edits to your photos. You know, when you rotate, fix red eye, resize & crop - that kind of stuff.
Basically, Vista saves a copy of your original photo upon import. Think of it as a negative - no matter how you develop your photos from the negative you can always resort back to the original. Learn more about it here.