I think this subject is still up in the air... Some of the girls have used the Kiwi Protect All spray before using their bags, some of us (including me) has sprayed our bags with Scotch Guard, some just use soap and warm water, some of us (including me) carry a Tide pen for on-the-spot treatments, and one girl uses the Sof Sole gel to clean her bags. Even with all of these, I think one thing is for certain... It doesn't seem that anything gets the bags 100% clean.
All of my bags, tokidoki and Coach, are always in excellent condition because I'm always conscious of what I do with them... So I think spraying with the Scotch Guard is just a preventative measure for me, and carrying around the Tide pen is just extra-cautionary. Otherwise, the only thing that seems to get my bag "dirty" is my clothing rubbing up against the back of my bags and leaving a gray patch that can't be removed.