UPDATES: First analyses point to an "energy magnitude" Me of 7.8 (later raised to 8.1) and hypocenter depth of about 35 km. CNN reported a 3-meter tsunami in Pago Pago, Samoa, which caused a good deal of damage. The Pacific Tsunami Warning Center reported a 1.6-meter tsunami there. Hawaii and the rest of the Pacific got a negligible tsunami.
The magnitude was raised from 7.9 to 8.0 by the USGS. Focal mechanisms are in at the USGS page; it was a normal event, meaning that the fault's hangingwall moved down upon the footwall. And the depth has been better determined at about 10 km.
The European Geofon seismic monitoring network put the magnitude of the quake at 8.2. An AP story cited 8.3 from the tsunami center's bulletin. Twitterers enthusiastically used the highest available number. But other than that, I must say that Twitterers passed around sound news and corrected themselves quickly. @Hypocentre pointed out that the various agencies are estimating surface-wave magnitude Ms (8.0), moment magnitude Mw (8.3) and energy magnitude Me (8.1).
The tsunami watch and warning was lifted six hours later. Hawaii has recorded tsunamis no higher than 50 centimeters. More than a hundred people have died in Samoa. As the aftershocks fade and Samoa resumes ordinary life, scientists will remain interested in this earthquake because it is very large for a normal-faulting event.
Friday, Chris Rowan posted a nice explanation of this earthquake and the Indonesian quake the next day.