A few near encounters, but the closest was on departure in IMC out of Brisbane climbing through about 800' and there to the left of the nose was a balloon! Missed it by about three metres.
The met office (BoM) release site is just off the extended centre line of runway 19, or was 13 years ago. Bizarre!
Biggest or most expanded was over central Australia at FL310 and it just looked huge off to the right of the aircraft. No deviation required in 8/8 clear sky.
halas