Andrew, The Mexican Zoom search facility sounds rather interesting.
I wondered some years back how easy it might be to request OIA 'request logs' from NZ agencies, and perhaps then make that meta data searchable. Having surveyed over 50 agencies I came away convinced that this was unlikely to be an option at that time.
Maybe in the age of the Public Records Act that's no longer such a pipe dream...

Been meaning to says thanks for your efforts on the OIA site Rowan. I'd dreamed of doing somethings similar years back , inspired back then by Alasdair Roberts and the Canadian CAIRS site, but never followed through with it.

Kind of sad that the recent OIA review only received around 20 submissions by its close off date though. The earlier OIA review, back in the 90's, was hardly flooded with submissions either.
http://www.radionz.co.nz/news/political/63813/20-submissions-received-on-oia-review