A number of people (such as Jeff Nolan) have suggested that Steve Jobs's announcement of the move to Intel will hurt Apple due to the Osborne Effect.
If Steve had announced that a G6 PowerMac or G5 PowerBook was going to ship in 2006, wouldn't that be just as likely to cause an Osborne Effect?
So even if there is an Osborne Effect, I don't think see why it should be attributed to the switch per se.
Mind you, given there are always new technological innovations, holding off on something you were planning to do now because of an announcement about a release a year away doesn't make that much sense to me. A quarter or two maybe. But not a year.
But then again, no one said the Osborne Effect was rational. Just that (some) humans think that way.