>>From my little experience (based on web browsing and reading), it seems these are good factors for achieving the above:
* All drive bays (HD/CD) at the front bottom of the system (this might interfere with expansion cards?)
* No holes in the case for air intake except at the bottom front
* Only air output would be the PSU fan
All the new cases just seem to have more and more case fans?! What's with that? <<
From my little experience, based on many heartfelt, but not all successful, mods, the direction being taken seems to be the right one.
The ideal place for a PSU fan appears to actually be directly above the CPU, sucking air from that particularly hot location and blowing it out over the supply. This has the added bonuses of causing the sound generated by the fan to bounce around inside of the case without providing a direct route out.
A lot of talk has gone into how many case fans you need. The general rule is that larger and more fans at lower speeds move the same volume of air as fewer, smaller, and faster fans, but do so at a lower volume. If you don't have any at all, you have to rely on convection to bring air in the bottom front of the case. PowerSpecs did this with my computer, and gladly replaced two dead, overheated motherboards before I took things into my own hands. To maximize convection you need to seal off the computer. This raises the ambient temperature inside of the case enough to get a hot-air flow going, which loweres the temperature of components being cooled by it. Cut air supply too much, and it doesn't do much of anything. Personally, I rely on fans for airflow, as fans can be silenced much more reasurringly than convection can be fudged.
The great problem with computing noise right now is still getting engineers to acknowledge that it exists and should be taken into account. Many motherboards are shipping with tiny, noisy northbridge fans that would be utterly unnecessary with a good heatsink. If it is cool enough to work, it is cool enough to pass muster, but many companies just don't think about how loud their componentry is. A cheap 80 MM case fan is less expensive than a slower, quieter 120 MM case fan. And those nasty, whiny 40 MM processor coolers are dirt cheap.