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I could be completely wrong (in which case I hope somebody corrects me!) but I believe the focuser issue Daniel is talking about relates to where the observer stands versus the direction from which the wind most often blows.
Let's say you live in the continental USA and the wind blows most commonly from the west. Most of your observing time will be spent looking at objects between the southeast, the southwest and the zenith. If, like most Dobs, your scope has its focuser placed on the right hand side as seen from behind the scope then you will spend the bulk of your observing time positioned on the western side of your telescope. While you observe the prevailing wind will tend to blow air warmed by your body across the light path of your scope (through the trusses and across the front). This warm air plume will decrease the local seeing within your scope and reduce the quality of the images you see through it. Of course, the whole scenario is reversed if you happen to be looking at something in the northern sky, e.g., Ursa Minor, and goes to pot if the wind is blowing from a different direction or not blowing at all.
In southern Australia I guess the wind also blows mostly from the west (more northwest in summer and southwest in winter?) but we are mostly looking between the northeast, the northwest and the zenith with our scopes. Therefore the common focuser position is good for this location.
How big a difference the above makes in the real world I don't know. Sticking your warm hand in a scope's entrance shows very obvious heat plumes so that part seems sound, I'm mostly not sure about how consistent the wind direction is, especially in Melbourne! Also, a shroud may help deflect warmed air over and under (rather than through) the scope but it does nothing for any warmed air passing in front of the scope.
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