I say the same thing every time this rumor gets rehashed.
Switching to Intel/x86 will break all third-party applications.
First, Any OSX-PowerPC binary app would have to be recompiled from source to create an OSX-x86 version. This version would then have to be tested and most likely "tweaked." This process is not free, and some software vendors would probably just drop OSX support altogether, because it would be a lot of work for a small market.
Second, this creates a split in the Mac market. Existing users would have PowerPC hardware; new buyers would have Intel hardware. Developers would have to decide whether to A) support only the new architecture or B) maintain two seperate Mac version of their software. B is expensive for the developers. A would alienate existing customers, who would not be able to buy new software for thier PowerPC machines
Third, existing customers have cllections of PowerPC software. If they purchased one of these new x86 Macs, they would have to pay to upgrade all of it.
Seriously, people. We've heard this before. It's a nice idea, but it's not practical. Even if it did happen, it wouldn't change things much: you'd still have to buy an Apple box to run OS X, and the Apple box would still cost more than a Dell box with the same x86 CPU, because Apple has to pay for OS X development and Dell doesn't.