I think that everything I've got is pretty well suited to everything else in the system, meaning that nothing in particular is slowing down anything when gaming, encoding, multitasking, whatever, but I think this forum would know better than I.
Currently I've got an Intel E5200 OC'ed to 3.33 GHz, 4 GB RAM running at 800 MHz, a ATI 4850 factory overclocked I believe, 2 Seagate 7200.10 or maybe .11 320 GB HDs in a RAID 0 array, all connected to an ASUS P5k-E wi-fi board. I'm in the process of backing everything up and upgrading to Windows 7 and thought this would be as good a time as any to look at potential upgrades. I do about 50% gaming (@ 1680x1050 currently), and 50% multimedia "stuff" with encoding video and such, as well as all your basic stuff.
It seems I have 2 upgrade options the way I see it. First is to go to a quad core at $150+ or so, which I'd hate to do as it's over twice the price that I spent for the E5200 which I've had for less than a year. The second, and more logical long term upgrade would be to go to an i5, but with new memory, new CPU, and new board it's at least a $500 upgrade that I don't want to invest in quite yet.
Really is anything in my current set up holding me back that much with anything that I'm doing?
Nah, your system looks good as is. Only some single digit percentage of apps can use more than 2 cores, and with Nahlem out, by the time you need Quad, you can trade one for a copy of the ET game. Although I will take this opportinity to preach the virtues of Nvidia. GT300 will be out soon, and the Fermi archetecture is totally C+ enabled meaning the GPU will offload the CPU in almost every scenerio, plus the full ECC support. So there, my only reccomendation is a GTX 360 when you feel like springing for one, and a core 2 quad after a year or two.