I would love to see stats on how many times delays like last Sunday's were avoided because ATCs gave up their days off to fill in. Personal experience leads me to believe there would be close to one a week (not just at SYD).
So for every time you experience delays - have a think about how many other times delays were avoided due to ridiculous amounts of overtime. If ATCs only worked their rostered 72 hour week, the massive holes in the system would soon be obvious to those outside ASA as well.
To hear idiots say that "we only need 889 ATCs and we have 960 on the books" just makes me spit. Like several years ago when the RAAF, realising that the category was almost 100 controllers under strength fixed it by simply "drawing down" CE at each base - voila, now we're fully manned!