Business Week presents an interesting theory:

There's only one Web. At least that's been the standard response in many tech circles to the emergence of the wireless Web. The point? No matter how you get online, be it by PC or smartphone, you'll still do the same things on the Web, using roughly the same sites and services. Really?
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Welcome to the weekend Web, where people are spending a bigger slice of time online via wireless devices—and using a different set of sites than during the workweek.

For a mobile marketer this presents many demographic challenges and opportunities. Read more at BusinessWeek.