If making a selection takes more than a minute, SAVE IT!

also save a selection if you want to key something for television. it has to have an alpha channel

As in all the work that you put your time into, don't forget to name everything you create!

I speak for myself, when creating a new selection (or layer, or whatever) I tend to keep the default name (layer 1 copy, etc... ;) ) as a result, sometimes after creating a number of selections and layers I spend more time finding out what they're all about than working with them...