Whitey, I rely mostly on long tail searches. The few I have checked (that feature most prominently in my logs) looked ok but there may be others that have dropped. It's impossible for me to go through all of them.
Regardless, there's no way it's just due to the public holiday. I've lost more than 50% of traffic. I doubt Australia Day would have caused that much of a drop.
No issues reported on webmaster tools. If my site was penalized would they tell me?