Just a couple of quick thoughts, as it's very late here.
1. As someone with experience in computer architecture and software engineering, it's my opinion that the x86 ISA really is a mess relative to that of the PPC. It is a tremendous credit to Intel (and AMD, for that matter) that they have been able to engineer processors that are so skilled at abstracting x86 code and delivering such performance using what are essentially RISC cores. The fact that we can talk all day about how ugly the ISA is itself, however, doesn't mean that the processors don't achieve very good performance by being elegant and efficient at a lower level.
2. It was mentioned earlier how forward-thinking it was for Apple to have secretly maintained an x86 build of OS X for the last 5 years. While it was fortunate, it's not that unusual a practice in the industry if you consider vendors of older Unix iron transitioning between different architectures or processor generations with varying ISAs (e.g. Sun, HP). It's good to have an abstraction layer firmly above the hardware and a good version of gcc.
3. Intel looked very good at the Stevenote, although I should say that IBM, for all of their recent trouble (or disinterest?) in designing/fabbing PPCs with higher clock rates and lower power requirements, are a powerhouse of design, engineering, and innovation as well. Many of their (fab) process innovations have been important in pushing along the performance of all kinds of ICs, microprocessors included (SOI, copper, etc.). So while we will have a lot to be happy about with Intel, we shouldn't fail to recognize IBM's strengths.
4. A lot of attention is being paid to the possibility (or the prevention thereof) of running OS X on a run-of-the-mill x86 box. I'm sure Apple will be able to make it difficult at first, but even if it happens, where is the concern? Presumably, the problem would be with Apple losing the revenue stream from Mac hardware. Well, if OS X really did take off in the general x86 space, and Apple could move up to a say, 40% marketshare (hard to imagine, perhaps), they really could start depending more on software as their income, along with whatever iGadgets they have in the pipeline. People will still buy Apple Macs, because they will be beautifully designed (as long as Apple wishes to continue making them), and they will be guarranteed to work with OS X.
5. If Apple's marketshare in the OS arena really did get that big, it brings to mind another possibility. If they are now in bed with Intel, perhaps Intel would be happy to have a robust, beautiful, general purpose operating system driving the sales of it's microprocessors. Whether those processors are in Apple-branded boxes may not be that important to them. In fact, if OS X really did eventually make it's way to all relatively-modern x86 machines (Apple-branded and otherwise), Intel really could stand to benefit a lot. At that point, they certainly would be a lot less dependent on whatever the wishes are of those in Redmond.
6. One final thought. This one is a bit silly, but cut me some slack, it's late.
Intel has a lot of money, far more than even Apple. If they were interested in either a merger, or some sort of takeover, it would be an interesting new marriage of the best operating system currently available and the processors on which it runs...all in the same house. Then _they_ (Intel/Apple) might be the scary monopoly. Imagine what might happen if they then decided to change their ISA just a little bit and stuck it to Microsoft? With all the problems with XP right now and Longhorn delays, the general public might really take to OS X, given the opportunity to run it, and provided they would have the applications they want run on it.
Just late night ramblings, I guess...but in summary, this was the right thing for Apple to do, given the delays (technical and possibly administrative) at IBM. This will give them the flexibility to use fast, low-power Intel processors and/or whatever they want from IBM/Freescale. Furthermore, it might be the gateway to a _lot_ more marketshare if they wanted it to be so...