For the ones I has Easter morning, I froze 'em. Washed and split them, rinsed again, spun them in a salad spinner to remove excess moisture, shook them in a bowl of flour, laid them on wax paper on a cookie sheet, and fast froze them. Next day just bag 'em up! When cooking, try to keep the butter temp fairly stable by adding the frozen shrooms a few (10-15) at a time to hot butter. Cook, turning as necessary, until desired crispiness is achieved. They taste like fresh-picked!
I also froze some unfloured ones for use in scrambled eggs, soup, or whatever.
Do you have any secrets or variations on the theme?