IBM already makes the G3 chip that is powering the machine I am writing this message with. Motorola makes the G4 and the G5, if it ever launches
The discussion about IBM is whether Apple will start using IBM's upcoming 970 processor. I think it's fine to have multiple CPU vendors. Even in the PC world they have Intel, AMD, and Transmeta. The thing is, in order for CPU vendors to be interchangeable, they have to support the same instruction set. Therefore, there's no way Apple will use both x86 and PPC chips. They have to choose one or the other, and as mentioned in another, thread, there's no wayy apple will alienate all their customers and partners by switching to a whole new architecture, especially when they just made a huge shift to OSX, and promising G5, G6, and 970 chips are just on the horizon.
Personally, I think Apple should definitely stay the course with the PPC. The next few months are going to be rough for Apple from a marketing point of view if Moto and IBM don't come through with new chips, but after that I think they'll be cruising. OS X performance should continue to improve, and with even faster chips the interface will be super-responsive. I mean, how fast does a computer need to be?
Personally, I think Apple is well positioned for the maturation stage of the PC market. It's like the early days of the auto industry. After almost every household already had a Model T Ford, and cars were already as fast, as big, and as cheap as they needed to be, then car makers had to start competing on features and design. Ford had a seemingly insurmountable market share lead selling their boring, generic Model T, until GM with its innovative designs and varied product lines started eroding Ford's market share, eventually overtaking it completely.
Since Apple has proven again and again that it has tremendous strength in product design, I would say it's in great shape for the future. Keep in mind the PPC chips help Apple add features to its computers: long battery life, low heat dissipation, quiet (or non-existent) fan. With $4 Billion in cash reserves, a sterling (and strengthening) reputation for innovation and product quality, and great new chips on the horizon, Apple can afford to ride out these rough spots and look toward a much brighter future.