I searched "cleaning iMac" for this forum and there was little or nothing about how to clean the new aluminum iMac. I already called my local Apple store and even they were hesitant to name a tried and single method for cleaning the aluminum.
Don't get it dirty. Seriously.
You are not actually seeing aluminum when you look at your new iMac. What you are seeing is aluminum oxide. Aluminium oxide is responsible for metallic aluminium's resistance to weathering. Metallic aluminium is VERY REACTIVE with atmospheric oxygen, and a thin passivation layer of alumina quickly forms on any exposed aluminium surface. This layer protects the metal from further oxidation. (The only time I ever actually saw aluminum metal was while I was machining it in a bath of kerosene.)
A number of alloys, such as aluminium bronzes, exploit this property by including a proportion of aluminium in the alloy to enhance corrosion resistance. You can remove the aluminum oxide with any abrasive cleanser and another layer of aluminum oxide will form as quickly as air touches the exposed aluminum metal. Unless you uniformly alter the surface of the oxide and polish out imperfections you will only achieve a splotchy finish.
Don't get it dirty.
Mother Apple says:
_Aluminum case:_ Damp lint-free cloth, water only. Wipe.
_Glass display:_ Damp lint-free cloth, water &/or iKlear. Wipe, don't spray.
...Caution: 2.4 GHz iMac not OSHA/EU approved for use in bathtub,