This hasn't been noded yet? Did I spell it horribly wrong or something?
I. Happy Holidays is a greeting-card catchphrase that aims to be inclusive of all winter holidays at once.
Do we really need such a barbarism? Well, apparently yes; some Jews actually get pissed when you wish them a Merry Christmas, for example. There's no sense in arbitrarily leaving people out of holiday wishes, when practically everybody has a holiday of some kind or other around this time of year.
Of course, even "Happy Holidays" fails because it is offensive to people who don't believe in holidays ("holy days"), to grumpy people (who don't want happiness), and to the clinically depressed.
For a truly milkwater goodwill expression, you must use "Season's Greetings".
II. Happy Holidays is also a holiday song!
Happy holidays, happy holidays
While the merry bells keep ringing
May your every wish come true
Happy holidays, happy holidays
May the calendar keep bringing
Happy holidays to you
(repeat forever)