There is this thread on PCLinuxOS Forum which talks about the Ext4 file system support on PCLinuxOS . I had a discussion about it with Neal . Neal has left a comment on this thread ( Reply #22 ) on September 22, 2009 which says that 2009.3 the next quarterly update CD will have ext4 support. Here is an unofficial "how to" for getting Ext4 on PCLinuxOS currently.
1 : Install the latest Kernel 126.96.36.199.tex5 and fully update your system from synaptic.
2: Format your root partition as Ext4 from the "drakelive-install" during installation and install PCLinuxOS to it.
3: To check and confirm that you have Ext4 on your root partition after installation use "mount" command in shell .
This can also be confirmed from PCC > Local Disks > Manage local partitions and click on the partition that you want to check. The file system type will be listed in the information pane along with size and mount point .
4: During next install if your root partition is formatted with Ext4 file system draklive-install will automatically pick and format it and get you Ext4 file system.
I tested it myself and it works flawlessly on my current PCLXDE installation. I recommend to give it a try and in case of on any issues report at the the thread I already mentioned above.