It's December 5, 2008 and – as promised – Microsoft has made the Vista SP2 beta publicly available. Early adopters can install it now and take advantage of improvements like 10% better power saving, reduced resource consumption in sidebar gadgets, Windows Search 4, and a long list of security and bug fixes.
According to Wired's post, you should be aware that you'll have to uninstall the beta in order to install SP2
final once it's released. Currently Microsoft is anticipating doing that some time in April 2009.