A couple of points everyone should be clear on:
1 - No Mac that you may already own with a PPC processor is going to be "obsolete" anytime soon. If you watch the Jobs keynote, you can see that developers will need to use Xcode 2.1 to get software working on Intel, and all software designed within Xcode will also work on the PPC G3/G4/G5 Macs too. It happens automatically during compilation of the new "Universal Binary" format. So software being designed to work on Intel based Macs WILL WORK on the current Macs too. Either not an either/or situation. It's both...automatically. (Any developer who doesn't support the Universal Binary format is just an idiot.)
2 - The "Rosetta" translation software that will be on Intel Macs lets all currently available PPC software run WITHOUT a recompile. That means any software you have today will work on a PPC Mac, or an Intel Mac, even if the developers go under or don't do recompiles. Your investment in Mac software is safe, no matter what.
3 - Phil Schiller said after Jobs' keynote an important thing: Mac OS X for Intel will only run on Apple-built machines, not Dells or Gateway, or custom built Wintel machines. This means that while Apple is going to run an Intel processor, it doesn't turn the Mac into just another "Wintel" machine. It will remain as unique a platform as the current Macs are...with OS X being the main draw, and the one thing non-Mac buyers still won't have access to.
4 - Although the Intel developer systems are going to be running Pentium 4 chips, neither Apple nor Intel announced that the first Intel based systems that will actually SHIP are going to be using Pentium 4 chips. Just like the Xbox 360 development system was a G5 but the final processor will not be a G5, the same can be said for Apple and Intel. Intel is working on dual-core chips, and low-power high performance laptop chip variants that are better than anything that is shipping today in any Wintel machine. So saying "I could have bought a PC today and got what Apple is going to be shipping in 2 years" is like saying "I can buy a 3.2 GHz P4 today, and in two years is will magically be whatever Intel is shipping in 2007." It's just not so.
5 - The 1-2 year transition period explained above also means that we can't automatically assume that Apple switching to Intel now means that the G5 performance sucks. Apple has documented benchmarks all over their site showing that TODAY, the Dual G5 2.7 GHz kicks butt over P4 systems. That fact hasn't changed. The only change is that Apple has realized that since IBM could not meet the 3 GHz promise Steve made at WWDC 2003 for 2 years now, it's more likely that 2 years FROM now Intel's chips WILL be better than IBMs. Again...it doesn't mean Intel is better/faster TODAY, it just means Apple has seen both IBM and Intel's roadmaps and is making a business decision based on who they have more faith in.
I repeat ... none of this makes anyone's investment in a G4 or G5 today ANY less valuable, or that a G4/G5 system today can't compete with the best Wintel desktops/laptops available right now. But Apple's plans are based on the future...and right now it seems that they have more faith on Intel's progress over the next 2 years than IBMs.
The best news of all is that if suddenly IBM found a magic lamp and made a wish for all their G5 production issues to evaporate overnight, Apple could decide to NOT switch to Intel. But at least they have the option...and the developers needed to know today "just in case".
It's a shock to all of us...our Windows hatred has always been directly attached to Intel, because of their synergy. But with Intel on Apple's side, as strange as it seems, it could further bring Apple closer to convincing even more people what we Mac users have believed a long time: That the Mac is the superior platform...not because of the processor alone, but the whole package. An Intel in a Mac doesn't make it a Windows machine...it's still a Mac. So we can all continue to enjoy the Mac vs. Windows war, even if the Mac vs. Intel war is finally over.