"Richard Gross, a geophysicist with NASA's Jet Propulsion Laboratory in California, theorized that a shift of mass toward the Earth's center during the quake on Sunday caused the planet to spin 3 microseconds faster and to tilt about an inch on its axis. When one huge tectonic plate beneath the Indian Ocean was forced below the edge of another 'it had the effect of making the Earth more compact and spinning faster,' Gross said."
Update, 11-Jan-2005: NASA Details Earthquake Effects on the Earth:
The "mean North pole" was shifted by about 2.5 centimeters (1 inch) in the direction of 145 degrees East Longitude. The earthquake also decreased the length of day by 2.68 microseconds.