[Update 11:45 UTC): IMPACT! LCROSS and the Centaur rocket have both impacted the Moon, apparently right on target. Ground-based reports are that no plume has been detected, but the observations from the Lunar Reconnaissance Orbiter itself, still orbiting the Moon, will be downlinked in a couple of hours. Keep your eyes on the NASA TV and the LCROSS sites (linked below) for more info.]
The LCROSS site is getting slammed so you may have a hard time getting in. Wired.com has a bunch of links to places covering the event live too, so try there and see if you an watch this very cool event as it happens!