They are intel designed processors but they are not Pentiums afaik. The Mac mini for example is using was is called the Intel Core Duo and Solo Processors.
The Core series of CPUs are merely slightly updated Pentium Ms (faster FSB and I think possibly a die shrink and bigger cache). The Pentium brand is getting on for what, 15 years old now? so I guess Intel decided it was time to introduce a new brand.
Core Solo and Duo CPUs are available in "standard" PCs as well, theyre not an Apple exclusive thing.
In any case, nothing has really changed for Apple with this architecture change. Yes, theyre using more common CPUs now but the OS is still different, there is a different set of software and you still cant run XP on them (at least not without a major bodge to get it going).