Just as an FYI, Best Skins Ever is the same thing as InvisibleShield at about a third of the price. With IS, you're paying for the warranty.
IMO, paying the shipping to send back your old/defective IS is not worth the hassle and I would rather pay the $8 for a brand new skin that ships in 2-3 days. You also don't have to worry about scratching your phone while you wait for the new one to come in.
On top of that, IS has horrid customer service (probably has a lot to do with their popularity) while BSE is very personal and accomodating. I sent them an email detailing how I had gone through several skins because of having to exchange my phone at the Apple store and they sent me two courtesy skins for being a loyal customer. When I used IS on my first gen iPhone and Blackberry Pearl, I attempted a warranty exchange for both. They refused my Pearl skin because I didn't return all pieces and my iPhone exchange is still processing (after almost two years, according to their website).