Great topic, and one that is certainly under-addressed.
IMO practicing your skills is extremely important.  True, your life is not on the line during practice.  But if you can't do it in practice under low-pressure, how do you expect yourself to do it for real under high-pressure?  Matt's analogy with EMS training is exactly right.  Before placing my first ET tube on a live patient, I had only done the procedure on manequins.  But if I hadn't done the "classroom" training I sure couldn't have done it right when it was for real.
Some think that they will magically do great when the shiite hits the fan.  But I urge those people to remember a proven adage from the world of combat: "you will not rise to the occasion, you will default to your level of ingrained training".
Note that we are talking skills here, not the proverbial mom-becomes-superman and lifts the car off of her baby.  No amount of "oh God this is for real" + adrenaline will enable you to build a fire or construct a shelter with skills you never knew.
Please understand I am not discounting improvisation and the ability to make-do with what you've got in an admittedly unpredictable crisis situation.  But I believe we need to apply a concept used by explorers, soldiers & others who venture into the unknown: be really good at what you CAN control and it will free you up to better deal with what you CAN'T control.