The Gentoo Qt team provides various live Qt ebuilds in our official overlay, qting-edge . These ebuilds now include x11-libs/qt-*-4.6.9999, building code from the 4.6 Qt branch, as well as a new USE flag called stable-branch, available (and enabled by default) in 4.6.9999 and 4.9999. This USE flag enables/disables the use of the stable branches, allowing you to choose between last-minute code VS tested, known to compile code.
Either way, its bleeding edge!
If you need help, leave a comment or visit us @ Freenode IRC, #gentoo-kde
 to install qting-edge, make sure you have layman installed and configured, then run
layman -a qting-edge.