Shiny side or not for foil?
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."