The upcoming version of xorg-server will have a lot of workarounds and patches removed. Doing so, the package becomes easier to understand, as even its maintainer has no idea what is happening anymore. When upgrading to xorg-server-1.6, you will see these file conflicts on most systems:
error: failed to prepare transaction (conflicting files) xorg-server: /usr/lib/xorg/modules/extensions/libdri.so exists in filesystem xorg-server: /usr/lib/xorg/modules/libwfb.so exists in filesystem
It's safe and advised to overwrite these files. The symlinks were previously created from post_install by the xorg-server and nvidia-utils packages. It is advised to install xorg-server first by using "pacman -Sf xorg-server", after which you can upgrade the rest of your system.
This release of xorg-server requires a rebuild of all video and input drivers. Older drivers will fail to load with an ABI mismatch. Drivers in our repositories will receive an update to match the xorg-server ABI.
Nvidia has updated their latest drivers with support for this version of xorg-server. AMD does not support xorg-server-1.6 yet in their Catalyst drivers. AMD users are advised to switch to the xf86-video-ati or xf86-video-radeonhd drivers instead, or keep any X.Org related updates on hold via IgnorePkg in pacman.conf. This can be done by putting xorg-server in IgnorePkg in pacman.conf. All other updates should have conflicts set, so it will be clear which additional packages should be added to the IgnorePkg list on your system. Note that there will be no support for older versions of xorg-server when this version moves to extra.