it's more a fact of the gpu being the more important component when coming to gaming and not the performance of your pc. If you are doing alot of pc gaming, you will need to look at getting a pretty good graphics card and a decent cpu(not the fastest or best). If you are doing more cpu dependent pc usage or you aren't gaming at all, you may benefit of having a pretty good cpu and a mediocre graphics card(since you're doing no gpu intensive work on your pc).
now with respect to a graphics card giving you more performance in things other than gaming, that will lie in the hands of two new platforms, CUDA and CTM. CUDA, nvidia's platform and CTM, ATi's platform, are both geared towards using the processing power of current gpu's to do usual cpu bound work on a pc. For more information on that, just google CUDA or ATI CTM.