Does it make any difference when you wrap food with aluminum foil for grilling or baking or making a steam pouch whether you put the shiny side in or the shiny side out?  I've seen at least one answer to a questiong about grilling that made mention of this. 
I've been told that the shiny side should go on the inside for cooking, and the outside for freezing.  In other words, do you want to reflect the heat into the food, or away from the food?  However, common sense (which fails very often) tells me that with the temperature ranges involved, any benefit is marginal, if it exists at all.    The only time it might matter, is if you were trying to warm something up in the sun.  Then it might make a difference.  EDIT:  From The Straight Dope:     The truth is that the shiny side is   not treated with a dangerous chemical.   Mineral oil is used as a lubricant   during the rolling process, some trace   of which may remain on the finished   foil--but it's not dangerous. The   shiny side is shiny because of the way   foil is made. During the last pass   through the rolling mill, a double   thickness of foil is run between the   rollers. The side of each sheet that   comes in contact with the polished   steel rollers comes out shiny. The   other side has a matte finish.   http://www.straightdope.com/columns/read/1135/should-a-baking-potato-be-wrapped-in-foil-shiny-side-in-or-shiny-side-out  ALSO     The official word from the Reynolds   aluminum people is as follows: "It   makes little difference which side of   the Reynolds Wrap aluminum foil you   use--both sides do the same fine job   of cooking, freezing, and storing   food. There is a slight difference in   the reflectivity of the two sides, but   it is so slight that laboratory   instruments are required to measure   it."  