Perhaps a mixture of both. To me I made the switch when I got both an iPod and an iPhone so getting a Macbook was somewhat a natural next step when I needed to get a new laptop. Didn't care too much about what's inside the machine, the different OS experience was a major concern at the time though.

* An Intel chip means that it's faster to run Windows (without the need for x86-on-PowerPC emulation).

* An Intel chip means that I can run Linux on it and still have access to closed-source programs (Flash, Matlab, etc).

* An Intel chip makes it possible to boot Windows natively.

* An Intel chip makes it easier for Apple to maintain forward momentum without needing to goad Motorola/IBM/etc to improve their PowerPC offerings to be competitive with Intel/AMD chips.

It's not as simple as that - they are a hybrid. An interface as easy to use as the previous Macs, hardware as cheap as a PC, an underlying OS as powerful as Unix.