There is of course a certain point where current OSes and apps give diminishing returns when more CPUs are used. There are also some studies that say beyond a certain point processing actually slows down for some tasks.

However, having four or eight cores is not a waste for many consumer desktops. I have an eight core MacPro with 10GB or RAM, running OSX (and often Windows and Linux in VMWare). OSX has a nice little dev tool where you can view the CPU load graphically, and you can disable CPUs as you wish - down to one CPU.

To make a point this weekend to someone considering whether to get a dual core or a quad core machine, I ran only an email client, a browser and iTunes - a typical consumer app load. In iTunes I was using a 'spectrum analyzer' visualizer which does load down the CPUs a bit, but it is not unusual for consumers to do something like this (or to be watching a DVD or streaming video).

At 8 cores not all 8 cores were used at the same time - it was switching between them. At four cores it was using all four cores simultaneously at about 25% average load each. At two cores it was using about 50% average load each. At one core the CPU was often pegged.

The point is that it doesn't much to load up current CPUs - even a top of the line machine like mine with an efficient OS can easily make efficient use of more than 2 cores with typical consumer use. Whether it is worth the extra money for a given consumer depends on their budget, their use and what they are buying. I have seen Dell quad core desktops on sale for under $500 so I don't hesitate to tell someone to get a quad core machine if the price is right. It won't be wasted and in the near future apps and OSes will take even more advantage of more cores.

I remember when the '386 first came out. A pundit in a review article said it would never be useful for the desktop - it would only be useful for 'file servers'. I also remember a couple of years after the Mac came out - another pundit asserted that Macs would never run Windows.

Never say never.

JeffA wrote:
No actual published benchmarks of typical computer use support your statement. I can point to dozens of articles backed by data on AnandTech, TechReport, Tom's Hardware, etc, that all show the same thing -- there is a *massive* point of diminishing return beyond 2 cores.

If you aren't in one of the narrow niches that can exploit parallelism, an ultra-fast dual core is all you need.
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If you are running benchmarks where you are looking at the performance of a single app, sure, many apps are not very parallel including not being very parallel beyond 2 CPUs.

However, if you are looking at the bigger picture where someone is using more than one app at a time, then you can start exploiting the ability of most modern OSes to use more than one CPU, to assign a given application at least one CPU.

It is not a 'narrow' niche to be listening to tunes or watching a video while something else is happening on your computer. Whether you email client is fetching email/RSSfeeds/etc., and/or you are burning a DVD, and/or you have an automatic backup process running, and/or you are downloading something. These are all typical uses that if you - the user - multitask - can find that you can easily put more than 2 CPUs to good use.

I bought my MacPro because it supported OSX (so I can run OSX, Linux and Windows, including 64 bit versions, all at the same time - I am a cross platform developer) and because it supports up to 32 GB (those VMs and DBMS servers and web app back ends take up a lot of memory) - not so much because it had 8 Xeon CPUs - but I did get the 8 CPUs instead of the 4 because I knew from time to time I could use them and in the near future more and more apps would take advantage of them.