It is better to have more cool air coming in that out. Also it is better to have an intake fan than an exhaust fan, you know what Im saying. True, for every action there is an opposite and equal reaction, and means that if your fans are taking in 100cfm then on the otherside its' exhausting 100cfm as well. But like I said it is better to force cool air in and direct them to the components that needs cooling than sucking them in using the exhaust fan.
Uggh, unless you're pressurizing your case, air in = air out. So your first statement is confusing. You recovered by saying the "every action" bit. Your statement about directing cool air onto the hot surfaces is a key point. Increasing the flow velocity on the hottest spots results in higher heat transfer. Adding conductive surface area (like a heat sink) at those hot spots helps too.
Ideally, you will have your case ventilation as a whole work with nature and not against it. Heat rises so there's no real advantage trying to work against that natural phenomenon. Thus, a blow hole fan - or at the very least, a top vent - makes good sense. Another way of thinking about this is that you don't want dead air spaces anywhere, but especially you don't want any up high because the hot pockets will transfer their heat to the components that are up there, like the power supply, optical drives, etc., and the upper part of the case. Not only will that add stress to those components, but they will conduct a portion of that heat downward through the case.
Exhausting hot air near the source makes good sense too, so the HSF on the X1900 graphics cards are a good design, as is the Zalman 9500 CPU fan coupled with a rear case fan aligned with the 9500's flow. Some cases blow inlet air right over the hard drive and that's a good way to keep the HD cool but it does add heat to the case. I added a pair of HDs a month or so ago and the case temp went up about 3 degrees C relative to the CPU temp - and the CPU went up about a degree relative to the ambient temp. The best possible ambient air-cooled case design does not exist in my opinion. What you would want is a case where cool air is blown directly onto each heat source and then it is immediately exhausted. And the components that generate the most heat such as the GPU, the CPU and the PS should have the most heat sink surface area and large corresponding air flows. It would be a weird looking case, huh?
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