We are now on the home stretch of the road to KDE 4.0, but KDE still needs extensive user testing to make sure everything arrives in the best possible shape for the release. There is a pressing need for users to be able to get hold of very up-to-date builds of KDE, especially if they want to participate in Krush days and pick up last-minute regressions, confirm proposed fixes, and avoid re-reporting recently fixed bugs, preferably without having to wait for their chosen distro to provide packages. KDE4Daily VM aims to provide such a service.
KDE4Daily is an experimental attempt at accomplishing the above goals using the Qemu virtualisation technology. End-users download the initial KDE4Daily 0.0.1 image (containing the now somewhat dated revision 734472), run it in Qemu and use the built-in installer scripts to upgrade the KDE 4 install to the latest revision provided, so that they can always test-out bleeding edge revisions pulled straight from Subversion. Upgrades are intended to use up relatively little bandwidth (20-50MB for a day's worth of updates is typical; bridge updates which condense a week's worth into one package bring this down to an average of 10MB or so) and be quick to apply (5 minutes per update is common, although bridge updates can take 10-15 minutes).
Because Qemu is distro-agnostic, you do not need to worry about distros or libraries or dependencies or suchlike; in fact, you can even test out KDE 4 while running Windows! The downside is that eye-candy such as KWin's new Composite-based effects will not be testable as Qemu does not support hardware graphics acceleration, and everything will generally feel a lot more sluggish than is the case with a native install.
An extensive FAQ is provided at the KDE4Daily homepage, above; please feel free to ask any further questions in the Dot comments section. Also, note that KDE4Daily has not yet had any real testers apart from myself, so please be prepared for "teething trouble" such as botched upgrades and bandwidth issues! Enjoy, and remember that the more people test, the better KDE 4.0 will be. As an added incentive for trying it out, you can try out the rapidly-developing Plasma as it progresses too!