Kubuntu has packages for 4.8 bringing updates to Plasma workspaces and a load of KDE Applications.
To quote a nice user posting on kde-devel
"I upgraded to Ubuntu's Precise Alpha 1 a few days ago. After the upgrade completed, I tried out KDE 4.8 RC 2. It worked great until the final release of KDE 4.8 Final. KDE 4.8 Final is even better than the RC!"
"KDE 4.8 is rocking for me too.Using the Kubuntu PPA's on Sandy Bridge system and it's just lightning fast to do anything. "