Arduino Day is a worldwide celebration of Arduino’s birthday being held on March 28. It’s a 24 hours-long event –organized directly by the community, or by the Arduino team– where people interested in Arduino get together, share their experiences, and learn more.
There isn’t much activity scheduled in Australia and, sadly, nothing public I can find in Sydney, but that doesn’t stop people setting up community events. Nor does it stop anyone just using Arduino Day as an excuse to do something cool, or just have a play with an Arduino. For what it’s worth the official Arduino Day website is here.
Anyway, Happy Birthday Arduino.