Xfce 4.8 stable was released few days ago. Release note read here.

For Ubuntu 10.04 32-bit and Ubuntu 10.10 both 32&64-bit, there are two PPA integrated Xfce 4.8 packages.

Alexx2000′s PPA (supports Ubuntu 10.04 32-bit):

sudo add-apt-repository ppa:alexx2000/xfce
sudo apt-get update
sudo apt-get install xubuntu-desktop

Koshi PPA (supports Ubuntu 10.10 both 32-bit&64-bit):

sudo add-apt-repository ppa:koshi/xfce-4.8
sudo apt-get update
sudo apt-get install xubuntu-desktop

After installation, logout and select this lightweight desktop environment session and back in.