It seems that a lot of us are having this conflict at the moment. I've been building my own machines since I was about twelve years old (so for about sixteen years). I'm not a hardware guy by trade, however; I'm a software engineer. Since I don't ride the constant hardware wave, I have to start from scratch before every new build to research what the latest and greatest are.
Until a couple years ago, this was no big deal. You find the fastest CPU you can buy right before the price-break. You buy it. Then you do the same with everything else. Or, like me, you splurge on the $600 top of the line video card.
But now, everything is different. AMD and Intel each have a dozen of their own lines with little variances in each. You don't intuitively know if one thing is faster than another, without loads of research on sites like this where you can read the experiences and look at the benchmarks of people who have been able to put them to the test. Then you get to choose from a dozen times of boards and a dozen types of RAM for each board.
But if nothing else, you knew that you could drop $1500 to $2500 on a new machine every twelve months and have the hottest, sweetest, top of the line machine that would perform double or triple your last machine the year prior.
But now, look at this. My AMD64 x2 3800+ from a year and a half ago benchmarks only about 20% below the performance of the latest expensive $400+ AMD or Intel chip. And even then, it probably isn't enough to push the rest of your rig to its limits (especially the 8800 GTX at the moment).
I see a lot of people around here telling us that they're upgrading from something like a 3800+ to a new 5200 or something. Why? That's such a minor improvement for so much money. I can't imagine building a new machine to replace an old one for less than double the performance. And most certainly not for 20% increase in performance!
I've spent the last ten days debating a new machine against my better judgment. You see, I'm used to playing all of my games with the highest settings at the highest resolution (2560x1600 on my 30" ACD with a 7800 GTX). But now that I started playing the MMORPG "Vanguard", I'm finding that I can't even get a consistent 25fps at 1200x800 on the same machine I play in highest-everything at 2560x1600 in Battlefield 2!
So I'm fighting my impulsive urge to drop $600 on the new 8800 GTX. But it seems that to get the most performance out of it, I'm going to be looking at going with the new Intel E6600 (or somewhere around there). Or perhaps one of the AMD FX chips. And there you get to buy a whole new motherboard and RAM.
I guess the "doubling every 18 months" thing is no longer true.