KDE 4.0 is not KDE4 but only the first (4.0.0 even non-bugfix) release in a years-long KDE 4 series to come.
KDE 4.0 is known to have missing parts or temporary implementations (eg. printing, PIM, Plasma).
Most applications (many are not even fully ported yet) will take only advantage of new features which the new Qt/KDE libraries offer later.
KDE 4.0 is only expected to be used by early adopters, not every KDE 3.5 user (and IMHO KDE 4.0 shouldn't be pushed onto other user types like planned for Kubuntu ShipIt (which by the way is said to have only 6 months support for its packages)).
Last, again: KDE 4.0 is not KDE 4.
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