I am soooo happy that Apple switched to Intel CPUs. Not because I care about x86 vs PPC, but because the new chips kick ass in general, and because they make one very cool thing possible.
First of all, Intel's Core Duo line is great. Having two cores in a laptop is incredible. I never thought I would see that kind of performance in a portable.
Secondly, the chips are great, period. I have a dual-G5 (2 GHz) and a 2.33 GHz Core 2 Duo MacBook Pro. Both have two cores and both are around 2 GHz so you might think that most things should perform similarly--but that's not the case. Using HandBrake to rip DVDs, the MacBook can convert a 22-minute Simpsons episode (H264, 2-pass encoding) in about 20-25 minutes compared to the G5's 60-80 minutes. That's an incredible difference. Performance on my 1.83 Core Duo MacBook is almost as good. (The MacBook is mine, the MacBook Pro is from work.) I can't wait to see what a Mac Pro desktop does. (I plan to buy one this summer--after new models are introduced--the 2.66 GHz Pro looks great, but it's a little pricey--and after new versions of OS X and iLife are out.)
The third and final great thing about Intel Macs is Parallels. Parallels is a program that lets you run other operating systems (Windows, Linux, etc.) on a Mac. Unlike Virtual PC, which had to emulate an x86 CPU, Parallels simply "pokes a hole" in the OS and lets guest OSs have direct access to the hardware. OK, maybe it isn't quite that simple, but the fact is that the CPU itself doesn't have to be emulated and there is a world of difference between running Windows in Parallels on Intel and running Windows in Virtual PC on PPC.
OSs in Virtual PC were always somewhat nonresponsive. Running XP on a dual-1.42 GHz G4 felt like you were using a 300 MHz computer at best. Parallels, on the other hand, feels like a 1- or 2-year old PC--surely not as fast as a 3 GHz+ gaming rig with a great graphics card, but every bit as fast as, say, a nice 1.0-1.5 GHz computer. Running Parallels on my MacBook in full-screen mode feels every bit as good as a recent Centrino laptop.
Also, having Parallels means I no longer need to keep a few old PCs around for playing with new Linux distros. I don't even have to burn CDs to test out the new distro-of-the-month--Parallels lets me install right from the downloaded ISO CD image.