I have seen the IS, and tried installing a BodyGuardz on a MacBook only to send it back. In my experience, the best price and the best skin is hands down the BSE - bestskinsever. I prefer to go back skin only as all these skins have a slight orange peel style grippy feel that is great for holding or nice in case and dirt gets in side your other case to prevent scratching.
As far as the screen goes, some people go full body with a skin, but in my opinion if you want screen protection, get a separate film style screen protector like the PowerSupport Crystal Film or Anti-Glare or the SGP Steinheil or Incipio films. They protect the glass, some give reduced fingerprints and glare and mimic the feel of the glass.