Here is the last version of Kubuntu, 11.04, also known as Natty Narwhal.
This release comes with important features such as a new kernel (2.6.38), the last KDE stable version (4.6.2), OpenOffice.org has been replaced by LibreOffice 3.3.2 (it is about time!), Upstart (0.9.7), LVM2 2.02.66 (very important for taking snapshots with LVM), Firefox 4.0.1 and so on.
It is significant to mention the new kernel, since fixes the Big Kernel Lock problem. Also point out the new Samba filesharing system, which allows easyly to share a directory in Dolphin, by configuring it through the Properties option.
My first impressions are very good, we have got a hardy and useful system, well worked out and really light.