"It is a real opportunity for Apple to tout the features of their operating system and, of course, the fact that it's available now."

Vista delay could add up to Mac sales

At the end:

Still, the company is slated to release Leopard, the next release of OS X, either late this year or early next year. That means it too could conceivably be on new machines before Vista.

I'll try not to gloat. (Have I mentioned lately how much I looooove Tiger?)