There will be no benefit at all placing one of these things near a CPU, but quite possibly problems if too close to the hard drive or other storage device. If the Shataki is magnetized in any way or emits any other kind of radiative wave, it can adversly affect the hard drive and serve to erase all your data in extreme cases! It could also interfer with your CRT monitor if too close.
The only benefit I can see, is that the Shataki may dampen vibrations from the noisy fans in the power supply and case -- this is one problems that Dell, et. al., could learn solutions from the audio crowd -- most computer vibrate too much and use cheap $2 fans that are very noisy.
Fixing a $2 fan with a $200 Shitaki is not very cost effective -- just go buy a quiter aftermarket power supply and case fan. ($120 for a good power supply.)That will do wonders for your sanity, as many people, myself included, put up with far too noisy computers. This is ironic in that I'm so neurotic over the slightest bit of tube noise or, God forbid, an unknown pop or click and didn't hesitate to spend big bucks for Bybee filters, PS300, etc. etc.
As for getting more speed from your system -- there are many books and mags devoted to just that. Most DIY hardware solutions involve overclocking, which can destabilize the system or cause it to run too hot. The best system optimization solutions are to simply fine-tune your OS, as most Windows and Mac systems are rarely setup correctly (they have too many programs in the start tray, a fragmented HD or other problems that cause the OS to run much slower than they are capable of). And if you have less than 128 MB RAM, buy some more --RAM is very cheap now.
Sorry for the transgression into the unholy world of computers, hopefully this will stop you from spending money foolishly. --Lorne