Gentoo comes with X11R6, the Xorg server 6.8 series.
However, with its release, Gentoo is migrating to Xorg 7.0.
I got a few errors with dbus and consolekit, which caused KDM to show windows without the resize/min/max buttons, and a few error message popups.
You must do the installation by starting your computer from a Live CD (A Linux environment with a collection of needed tools).
The whole process is described in detail in the Gentoo Linux Handbook.
this is bad because mixed versions of Qt packages (like qt-core-4.5.1 alongside qt-svg-4.4.2) can result in unexpected breakage.
unfortunately, at the moment this error is the only way we can prevent version mixing.
Xorg 7 is fundamentally different because its previous few packages have now been much split to form around 100 new packages which constitute the server.