In New Zealand we refer to these as "As-And-When-Required" agreements, and while they are very common in seasonal situations, it is not uncommon for them to apply all year round.
For us they bring particular legal issues particularly around payment for public holidays, as well as where the days and hours establish a 'regular' pattern.
They are most common in workplaces that can be adversely affected by the likes of weather; availability of product; storage space; etc.
One of the adverse aspects of zero contracts reported in the article was people not knowing what their income would be for the week or fortnight. Here, we tend to address that by stipulating a minimum weekly/fortnightly payment, but that was not mentioned. There was also quite some emphasis on the propensity to dim loyalty/employee engagement/enthusiasm about work.
I would be very interested to read the experiences of members of HRZone.
Cheers. Don Rhodes.