Apple announced today that beginning in 2006, new Apple computers will run not on IBM's Power PC chip, but on Intel's chip. The transition is brought about by IBM's failure to deliver higher speeds (the 3gig G5) and more importantly Intel's development plans that produce more productivity with lower power wattage usage--think powerbook. They actually confirmed that Marklar exists-from the beginning, OS X has been written to compile on both PPC and Intel all along.
Really, this means very little to you, typical bible scholars and pastors. It does mean that Macs will get faster quicker and/or possibly less expensive. Newer version of applications will be able to run natively on both older PPC computers or Intel machines. But still, your "old" OS X apps will run on the newer processors via a tranparent translator (which they've named "Rosetta"!) without any performance or speed issues. It will be the end of 2007 before Apple before the entire Macintosh computer line runs on an Intel Pentium processor. It means that apps that currently run only in Classic mode might be left behind (until someone writes a new emulation).
For others, especially developers, it means more. It most likely means the death of PPC Linux.
Don't get crazy with the speculation, as does the oft-pleasantly-inciting Ken Ristau. This does not mean that Mac apps will be running on Windows, or vice versa. The applications run off of the OS kernel and API calls, not the chip alone. It will not be possible to run OS X on a generic Intel box, nor Windows on a Mac Intel machine. The combination of custom asic, Apple's nonstandard, nondocumented chipset, and most likely some form of DRM will allow Apple to maintain its control. Speculation is that it might be slightly more possible that the hackers will be able to get Windows running on a Mac Intel box.
It does mean that older applications which fall in the 25% of Mac apps that are currently coded other than in Xcode (Ac*cough*cough*cordance*cough*) will have to do some extra work to transition towards the new Universal Binary. But not immediately. For the next few years, they'll simply still just run.
All in all, it is an exciting day for Mac users.
Followup: I think it's worth repeating quotes from a C-Net interview being discussed in the comments to this post.
Apple Senior Vice President Phil Schiller addressed the issue of running Windows on Macs, saying there are no plans to sell or support Windows on an Intel-based Mac. "That doesn't preclude someone from running it on a Mac. They probably will," he said. "We won't do anything to preclude that." However, Schiller said the company does not plan to let people run Mac OS X on other computer makers' hardware. "We will not allow running Mac OS X on anything other than an Apple Mac," he said.Microsoft won't be making Longhorn so that it can't run on a "Macintel" computer, but you better believe Apple will be doing everything they can to prevent hacks allowing a beige box bootup of OS X.