Update: 12:05 Hawaiian Tsunami has begun, could have peaked or may become more noticeable, so far so good though. About one meter.
Update: 11:56 Big island reports it is now registering on gauges. ~ 3 feet.
Hawaii should be seeing the first Tsunami in a few minutes. Waves are predicted to be between 1 to 3 meters on south facing shores. If those predictions are accurate, this shouldn't be a devastating, full blown national disaster event or anywhere near it. With the possible exception of people dumb enough to run down on or near waterline to watch it -- Note that NOAA is saying the water could go as far as one mile inland in places -- those who heed local warnings and move to higher ground should be at no risk. And there is reason to hope it ends up being much ado about nothing.
But that was a big earthquake and waves are flaky phenomena. Waves bend around islands and roll across unseen under-sea topography and go on to diffract and interfere with each other, causing waves to bunch up in some places and flatten out in others. The actual force and height at a specific locale is not easy to predict. One thing that makes this one unique no matter how big or little it ends up being: it will be the best documented Tsunami in the history of the world.
Below in the first comment I've posted some footage from two similar events in 1946 and 1954 respectively. While the actual heights of the ones portrayed are not exactly known, the video gives some idea of what Tsunamis actually look like.
Update: First reports of water receding in Hilo Bay at 11:15 Hawaii time.
Update: First reported surge signs in Hilo Bay at 11:25, doesn't look like much. But I don't think this thing has hit yet guys.
Update: 11:45 Hawaii local time. There is some speculation it's delayed by up to an hour. Unconfirmed.