As of today, Kubuntu 10.04 users can upgrade immediately to the KDE Software Compilation 4.4.3 to ensure they are running the latest and greatest KDE Desktop. Per the release announcement, this release is not a feature release (as 4.5.0 will be) but rather
"concentrates on stabilizing the existing codebase. As such, the upgrade should be safe and painless, so we recommend updating to everyone running previous KDE SC versions."
A blog post over at Free Techie details how to quickly and painlessly upgrade your Kubuntu installation.