I'm running Slackware64-current with KDE-4.4.1 - its very slick and well-polished. KDE is definitely getting better.
I have been using -current myself. With the progress that the KDE team has been making it really looks like they will be offering good competion to the windows and mac user interface developers. Their work may be what is needed to push Linux based systems to being accepted for desktop use by regular users.