I've not read much online about this yet, and I've not watched the full keynote, so I could be missing something.. however, I thought I'd throw out some predictions about what this means..
First, I don't think it means Apple hardware will be getting cheaper. Steve didn't say that cost was a factor in the decision to move to Intel, he said it was better plans for features. Apple have never used cost as a differentiator; they use design, ease-of-use, and brand recognition instead.
My prediction: Apple will have Intel create new features that only Apple have access to, thus keeping them differentiated on features.
Second, I don't think this means you'll be able to buy a copy of OS X and whack it on your existing machine. Apple isn't a software company, they're a hardware company. Perhaps you might be able to buy new Mac hardware and run Windows on it - but then, Windows already runs on G5s. Steve only said that Intel would make their CPUs - he didn't say, at least in the parts I saw, that those CPUs would be Pentium-family.
I'm going to go away and work now. Expect my rant about SW:RotS later tonight.