My theory is that once CPUs hit the Gigahertz mark, CPU speed became irrelevant. RAM is slowly but surely becoming like this, within the past year or two, it has become quite feasible to stuff your motherboard to it's max capacity of RAM without having to re-mortgage your home.
I think this is going to kill the PC market as we know it. There used to be a time when there was a tangible benefit to average people to buy the latest and greatest computer. Now there just isn't. Also, now that PCs can handle just about every form of multimedia under the sun, there just isn't that need for more powerful machines. Manufacturers are struggling to convince people of the merits of things that they don't need. Gaming is the main driver of demand for high end hardware, but sadly the PC gaming industry is a shadow of what it used to be. As consoles become more popular and capable, I think PC gaming will become more and more of a niche market, and thus not as influential as it used to be.
MS artificially pushed along the hardware market with bloat and (probably deliberately) poor quality OSes, but people have long since copped onto the game, the result of which is Windows 7 - a real throwback to the spartan Windows NT days. I'd say that Windows 7 will be kicking around for a long time, probably longer than Windows XP (basically a downgrade of Windows 2000) so MS now really has to go out of it's way to make it worth people's time and money to adopt a new OS.
Now of course, most of the things that 99% of people need computers for are now hosted elsewhere, so the computer is little more than an appliance for accessing the internet. It's almost cliched at this stage, but the cloud is where it is at. And alot of the traditional establishment is rather scared of things like smart phones and netbooks. The problem here is that people don't need or want fancy PCs, a fact that is exacerbated by the fact that a lot of services have moved to the net, and thus the market share of more profitable machines has taken a huge hit. Intel dislikes the Atom because its eating into the potential target market for it's higher end chips. MS is trying to castrate netbooks with things like Windows 7 Starter Edition and XP licences that restrict how powerful of a machine it can be installed on. In effect, they are telling people how they should use their computers, and what for.
I think it will come back to haunt them. Once ARM releases their dual-core CPUs, and Google comes out with it's Chrome OS, I'd say the likes of Intel and MS are going to have some pretty serious problems. People don't need bloated 1990s workstation OSes and Quad Core CPUs, they want something to read mail, download porn and whatever else takes their fancy.