Hi Gift,

thank you for your input; I read the whole thread and I am now more confused than before :)
Even without going to complex modules, i see that some simple dnn sites (or even some skin demo sites) do not refresh the entire page when browsing them, for instance. It looks to me that those sites are implemented "out of the box", if I may say, and I doubt those webmasters went through the pain of adding the UI code. Instead, all my sites (except one or so) go through the entire page refresh, even when having just static html modules. Does it mean those other site do not run in medium trust, perhaps, whatever that means?

Some modules may make ajax requests and dynamically refresh part of the page. There is no wholesale way to do that for a page though. Concentrate on page speed (plenty to find doing a google search) or resort to some jquery fadein/fadeout approach on the body tag.