The official KDE 4.4 packages have been uploaded to a PPA for Karmic. To set it up follow the instructions on the kubuntu backports PPA page.

On that same page, you'll find the full list of packages that are in the PPA. By selecting individual packages, you'll find their description and changelog. For the full KDE desktop, the package you want to install first is kubuntu-desktop.

To compare versions across all distributions, repositories and PPAs, you can do a package search. Here is an example for kate, one of the best if not the best text editor available in Linux.

kde.org has a great overview of the new release.