More and more games are being multithreaded. I predict that the next hot titles to come out will be almost exclusively multi-threaded and you will need the quad core to play the games with all the bells and whistles on. Even games that were not originally multi-threaded when they were developed are being optimized for multiple (more than 2) cores via a patch. FSX is an example of this. If you don't think you're going to buy any more games in the future, buying the core 2 duo might save you some money to play yesterday's games. If you have the money for quad core, I think it is a worthwhile investmentment.
Rob
The immediate hole in that theory is that no game (or even new must-have application) will have shipped that requires more than two cores between now and the expected halving of Q6600 prices (a mere three months out). E6600 today is $236USD (local retail); it was $306USD (same dealer) two months ago (and that was a sale price, while the current price is the new retail number). Q6600 in Q3 will likely be no *worse* than $285USD (again, same dealer), while the E6600 will not only see pricing remain flat, but it will basically be discontinued. Paying over twice as much for two extra cores is no bargain; however, paying less than $50USD more for two extra cores (even if you don't need them most of the time) is a major bargain.
Also, there are other reasons to seriously consider multiple cores; how many people run only one application at a time these days? If you run so much as two IMs and a P2P application in the background at all times (and that would actually be considered *light*), you are a genuine candidate for a multicore CPU today. For each additional two applications you add to the combined load, you can safely add the processing power of another core to your real-time processing loadout. I pretty much stopped running one application at a time when Windows 2000 (and Intel's NetBurst Architecture) were still new (remember, Hyperthreading hadn't gone real-world yet). And don't even get me started on the power required to run productivity applications (such as OpenOffice.org, browsers, or e-mail apps). It's not just multi-threaded applications or games; but multiple single-threaded applications/utilitities running at once that also seriously call for a multi-core CPU. (And *that* sort of processing load is a lot more commonplace than people will want to admit; take a good look at the tasktray of your OS of choice (even, perhaps *especially*, if you are still running Windows XP); add one core for every three icons in that tray.)
Its not really that big of a deal. I'm on vista and as i write this, one core of my 6700 is idle and the other is @ 1%. I have 8 programs in my system tray, limewire, and this iexplore window open.
Now, I DO understand your point. I was playing some BF2142 the other day, smooth as silk. I looked down and saw that my hard drive is going crazy. That usually doesnt happen. So, I duck out of the game to see why my disk is accessing like a mofo. Turns out, my defrag was running AT THE SAME TIME as my McAfee decided to do a full virus scan.
No performance hit to my game whatsoever. That's just with 2 cores. I was kind of floored for a minute. Then I told her she's a good girl and went back to fraggin noobs.