Pretty good summary from Russell Brown:
http://publicaddress.net/hardnews/the-solemnity-of-the-day/
Basically, from midnight Friday till close of polls, it's a crime to publish any statement that could influence another voter.
That applies to canvassing, hoardings, wearing a tshirt advertising a political party (certain election day workers like scrutineers are allowed to wear a rosette AFAIK), publishing anything in the media, on radio or TV (publishing things like "polling places are busy, John Key just voted at his local polling place etc is fine, but nothing about policy etc), or as we've seen now, on FB, Twitter or any online thing. You could face up to a $20k fine.
It's a serious matter, it's nothing remotely to do with free speech or anything like that, it's been law since roughly 1905, and is all to do with (as Brown's blog and the articles he links to mention) protecting the solemnity of the day. Basically, don't be a dick and let people go about their voting in peace.
Possibly a good idea to lock the election threads on Saturday?