...from: http://www.macworld.com/2006/01/features/intelfaq2006/index.php

[...] So there’s an Intel chip in a Mac. Why should I care?

If you’re a casual Mac user, you shouldn't care. If you sit down at an Intel-based Mac, it’ll still feel exactly like a Mac. However, the transition to Intel chips will affect many Mac users, especially those who rely on older software that hasn’t yet been updated for Intel-based Macs. And the Intel transition will have a long-term impact on the Mac world, affecting the design and speed of new Macs for years to come.

[...]

Okay, so… Core Duo. Is there also a Core Solo?

You’ve been peeking. Indeed, there is—Intel’s got a lower-power, lower-heat sibling to the Core Duo called the Core Solo. When we asked Apple about its choice of the Core Duo for the iMac and MacBook Pro, company representatives said that “using dual-core processors for these products was exactly the right thing to do.”

Of course, when Apple makes statements, you’ve got to parse them carefully. What we took out of this statement is that you might see a Core Solo processor in some other Macs in the future—ones that don’t need the power of a dual-core chip. For example, future Mac minis, iBooks, or even ultra-light notebooks might be candidates for such a chip. But that’s sheer speculation on our part. Intel’s got lots of chips. Apple will use some of them

[...]

Will Classic mode run under Rosetta?

No, Classic mode won’t run on Intel Macs at all. If you still rely on Classic applications, Intel-based Macs aren’t going to work for you. This would probably be a good time to begin investigating OS X-native alternatives to the Classic programs you’re currently using.

[...]

Now that the first new Intel Macs have come out, should I go buy one?

It depends. Our lab tests indicate that an iMac Core Duo does run native applications 1.1 to 1.3 times as fast as an iMac G5, and performs even better with applications that take advantage of multiple processors. And if you've gone a few years between iMac upgrades, you’re likely not to even notice the performance hit when running applications with Rosetta.

For more on whether this is the right iMac for you, check out Henry Norr's review of the new models.

[...]

Can these Intel-based Macs run Windows?

Ask people from Apple this question, and they’ll do one of two things: shrug, or plug their ears and pretend they can’t hear you. Basically, Apple’s official policy is that if someone wants to figure out how to run Windows on a Mac, they can go ahead and do it, but Apple doesn’t want to know about it.

One interesting quirk of these new Intel-based Macs is that, unlike the developer test systems released last summer, these systems use Intel’s Extensible Firmware Interface (EFI) instead of the tried-and- true BIOS that classic PCs use. Windows XP doesn’t actually support EFI, although the forthcoming Windows Vista will.

So the question is, how will people get Windows to run on the Mac? We’re sure someone much smarter than us will figure it out. Whether you’ll be able to re-boot into Windows or run it in some sort of compatibility box—hello, Virtual PC!—remains to be seen.