Since the mid 1990's, the New Zealand government has pursued a policy of indefinite detention without trial against those claiming refugee status or who cannot be deported from New Zealand. The policy was cruel, inhumane, and violated fundamental human rights; it was also completely ineffective, an exercise in pointless sadism. And following the outcry over the detentions of Iranian refugees Thomas Yadegary, Ali Reza Panah and Amir Mohebbi it seems to have been largely discontinued. On 23 May 2007, there were 51 people detained under the Immigration Act, the longest for more than three years. But according to documents released under the Official Information Act, that number had dropped to four on 1 March 2009:
(s59 allows someone to be detained for up to 72 hours pending the execution of a removal order; s60 (6) (a) and (b) require detention for those claiming refugee status after being served with a removal order, and those who are refusing to cooperate in their own removal)
So, a 90% reduction in the course of a couple of years simply because people started paying attention. I'd call that a success.
It may be short-lived, however. The government's new Immigration Bill - still on the Order Paper, though not a high priority - would massively extend detention powers and entrench the use of secret evidence in immigration cases. So having finally backed away from an evil and pointless policy, the government looks keen on repeating it.
Correction: Corrected basic maths failure.