>I feel that the client not paying constitutes nothing more than piracy,

And you would be correct. So sue the client for the money you are owed.

> so
>I was wondering if you could give a bit more info on this precedence,

I don't remember the details, I don't even remember who was vs. whom. I just remember that this very scenario came up in the U. S. court system at least once, and the company that put the time bomb in the software lost.

> as i'm
>sure that Mark isn't the only one who puts such "features" into their apps.

And they would stand a good chance of losing if the client sued in the U. S. I imagine that you may succeed if the time bomb conditions were stated in the contract, but IANAL.

>Can anybody say Office XP :)

That's an entirely different scenario and does not apply here.

>I think you could also argue that there is legal precedence for not being
>allowed to use something that you haven't paid for.

Yes, there is. However, according to the U. S. legal system, you are not allowed to be the judge, jury, and executioner in such cases. YMMV in Australia.