FURTHER TRAVEL DILEMMAS:  Following up on our discussion about "why don't hotels offer toothpaste," another hotel amenity question--why do most hotels invariably offer a shower cap?  Does anyone actually use the shower cap?  Is it a requirement of hotel grading to offer it?  Have the titans of the disposable shower cap industry somehow entered into a nefarious bargain with hoteliers under which they are guaranteed the opportunity to supply the shower caps to America's hotels?