After a lot of bug-wrangling both by upstream and by our Qt and KDE teams, we now feel confident that Qt 4.7.2 and KDE 4.6.2 are ready for stabilization. If you are a stable tree user (amd64, ppc, x86), the upgrade from current Qt 4.6.3 and KDE 4.4.5 will arrive at your machine soon, with lots of new features. (The KDEPIM applications such as kmail, kontact, or akregator will stay at trusty version 4.4 since development there is still ongoing.)
As a special bonus, the stable upgrade will also include newer versions of several popular applications that take advantage of KDE 4.6 features. These include Digikam 1.9.0, KOffice 2.3.3, and KDevelop 4.2.2. There is a new bluetooth framework called Bluedevil, we no longer need HAL, and, and, and... :)
The upgrade should go very smoothly; if you encounter any problems, we have a specific Gentoo KDE 4.4 - 4.6 upgrade guide to help you with that. In addition, there is always the Gentoo KDE guide with general tips and tricks.
Thanks to everyone who made this possible!