According to the announcement, the update opens the door to providing OpenVZ under Ubuntu, since Ubuntu's upcoming Feisty release uses the 2.6.20 kernel. The Feisty beta release already includes a vzquota package, which contains tools for managing quotas under OpenVZ.
Unfortunately, the OpenVZ project is still packaging OpenVZ kernels as RPMs only, and no OpenVZ-enabled kernels are available for Ubuntu yet -- so Ubuntu OpenVZ users have to try to patch a vanilla kernel to use on their systems.
The announcement also lists additional improvements, including the ability to prioritize I/O for virtual environments. This provides the ability to give some VEs higher priority for disk access than others, which may help alleviate performance issues for VEs that run applications requiring heavy disk access.