KDE 4.2 Beta 2 was released on 18th of December by the KDE community. As per the announcement 1665 new bugs have been opened, and 2243 bugs have been closed since the release of Beta 1.
If you are using ArchLinux you can grab the KDE 4.2 packages from the kde-unstable repository of Arch Linux. Though the repo is not announced yet, the KDE 4.2 Beta 2 packages (4.1.85) are available in all the mirrors.
Just add the following lines to your /etc/pacman.conf file.
[kde-unstable] Include = /etc/pacman.d/mirrorlist
The lines have to be added above all the repositories core,extra and community. You will also need to enable the [testing] repository as the kde-unstable packages have been built on the packages from testing.
After adding the above lines to pacman.conf, give the command pacman -Sy as root.
Then give the command pacman -S kde to install the full KDE 4.2 Beta 2 packages or pacman -S kdebase-workspace to have a minimal KDE 4.2 environment.
I am installing KDE 4.2 Beta 2 now. I will write about my experience once I try it out. 
Paul
9 Jan 09 at 9:46 am
I don’t understand why you have to add the kde-unstable repository before core and the others. Isn’t pacman supposed to install the most recent version of a package?
Manas
11 Jan 09 at 11:44 am
I guess pacman should do that.
But when I place kde-unstable below all other repos, pacman picks up KDE 4.1 to install. So I suppose pacman installs the version which it finds in the first repository.
Paul
11 Jan 09 at 11:40 pm
Which I think is rather naive.
fast_rizwaan
12 Jun 10 at 12:40 am
#i just added the following 5 lines to /etc/pacman.conf just above [core] section
[kde-unstable]
Include = /etc/pacman.d/mirrorlist
[testing]
Include = /etc/pacman.d/mirrorlist
#after saving the pacman.conf, run pacman -Syu.
# vhba-module was not required so i removed it
sudo pacman -R vhba-module cdemu-daemon cdemu-client
Thanks for the info. I could