Working with the Virgo Collaboration, which runs a gravitational wave detector near Pisa, Italy, the LIGO team has now analysed what their own detector saw between November 2005 and September 2007. Although LIGO did not find any waves, the teams conclude in Nature1 that the SGWB is even smaller than LIGO can currently detect. This result rules out some theoretical models of the early Universe that would generate a relatively large background of gravitational waves.
A news story on this can also be found at MSNBC website. It has a good description of LIGO and how it can measure gravitational waves. Anyone wanting more detailed description of LIGO can read one of my previous blog entry on this facility/project.