It's not a huge endeavor to protect your bike's frame from the Winter elements, however it is a very important step in the process of Winterizing your bike.
Basically when you do this process, you're protecting your bike's metal parts that are have the possibility of being exposed to the elements. The estimated time to run through the routine of winterizing your bike frame is about ten to thirty minutes.
To protect the metal parts of your bike for Winter, simply spray the exposed metal parts of your bike with a good rust inhibitor such as WD-40, Cosmoline, or Maximas Chain Wax works well.
Doing this simple step will prevent rust and corrosion from happening on your bike frame during the Winter months and it can set in faster than you might think. You just need to make sure that you do a thorough job removing these chemicals that you apply to the frame when you want to ride your bike again in the Spring.
If you do see a rusty spot on your bike frame, you'll want to spray it well with a rust inhibitor at the very least and most likely address the rusty spot and prevent it from doing any more damage to your bike during the Winter storage time.
Also, if you happen to get any ChainWax/WD40/cosmoline/whatever rust inhibitor you chose to use, on your bike's parts. You can do a little spot washing to remove the chemicals and insure they don't wreck the finish of your bike while it is in Winter storage.
A fast way to remove these chemicals is to use a diluted solution of a degreaser, organic or otherwise,it's your choice. Simply spot clean any place you've gotten a rust inhibitor on your bike that the chemical should not have gone. This will insure that you have a well maintained and long lasting bike that will give you years of good riding fun, even after Winter storage!