The New York Times has an interesting piece about Apple's switch to Intel, and says that IBM was one of the last to hear about the deal. While it may be technically true that IBM was told of the final decision from Jobs just a few days before the keynote, it's clear that negotiations with both parties had been going on for quite some time. (Now we finally know what Otellini, CEO of Intel, meant when he suggested those interested in security might want to try a Mac.)
While Steve Jobs talked in his keynote about the uninspiring roadmap and performance per Watt worries for PowerPC, the NYT sources suggested the main issue was chip pricing. In other words, they suggest business and economic concerns were the overriding issues, not technical. I don't really see this as being necessarily separate. IBM is no slouch at chip design and chip fabbing, but it's clear that they had not been able to meet Apple's needs with the resources at hand. For IBM to be profitable on this deal, they would have asked for more money to meet Apple's speed and power goals in a relatively short time, but Apple simply balked at that idea. Basically it was likely a combination of both financial and technical concerns.
However, I'm guessing that IBM actually knew something about the Intel talks, but thought like I did, that switching to Intel was simply too crazy to consider at this point, and that Jobs was merely using the Intel talks as a negotiation tool with IBM. IBM probably thought he was bluffing, and overplayed their hand. Mind you, it's not as if IBM had a choice anyway, if they were not going to be profitable under the terms Apple wanted. On the other hand, if IBM had truly been in the dark about the latest round of talks with Intel, perhaps it was because Apple simply didn't care to negotiate any longer with IBM if it felt that no acceptable deal could possibly be reached. If so, that's simply good business. However, like I said, it's likely that IBM knew all along that something was up. We shouldn't forget that IBM bragged that they kept Intel out of the Mac the back in 2003.
Also in the article there is mention that Apple spoke with Sony about Cell, but felt that the chip was inappropriate for Macs. This is not surprising, since Cell isn't built as a chip for general desktop computing. While OS X has likely been tweaked already to run on Cell, its anemic single PPE unit and unsupported SPE units made use of this chip both unfeasible and undesirable. This random forum post claims IBM was also actively pushing Cell at Apple, but Apple just wouldn't bite, and for good reason.
In the meantime, there are definitely still deals in place to ensure some supply of new PowerPC chips for Macs are forthcoming. Jobs told us himself during the keynote. With regards as to what those chips are, Freescale has already said they will be releasing G4 chips for the Mac mini and iBook. Curiously no mention of the PowerBook (or eMac) is made, despite the fact that the G4 7448 would be the perfect drop-in upgrade for the PowerBook. Could a G5 PowerBook still be on the way? Given Jobs' remarks about (the lack of) such a beast, I'm not confident we'll see one. However, I still do expect to see dual-core G5 970MP machines (including possibly the quad) released in the coming year. The Power Macs are the most in need of stable and native software support that the G5 will offer during this transition period, and consequently Apple would probably like to keep them around as long as possible. I would not be surprised to see two more iterations of the G5 Power Macs, including at least one 970MP model.
We may never know what truly happened behind closed doors with Apple and IBM, but as long as Intel can keep up their end of the bargain and Apple can make the transition relatively painless for its customers, that's all that really matters.