Dan, you said that this quake affected the rotation of the earth. Is this something that we'll be able to notice at all? Like daylight coming later or something?
Probably not. We're talking about milliseconds here.
What are the chances of something like this happening again?
Once every 30-40 years. On average.
Would a quake that size be capable of making California an island?
No, but this quake repositioned Sumatra 120 ft south of where the island formerly was. It was this sudden movement of this large landmass that affected the rotation of the earth. It would take hundreds, maybe thousands of earthquakes like this before California could even begin taking the form of an island. Besides, the tectonic forces working in California are different than the forces working near Sumatra. Strike-Slip forces are at work in California while Convergence is at work near Sumatra. Neither of these forces will split a piece of land from a continent quickly. It takes a divergent boundary (spreading centers or rift zones) to create such a scenario.