Fairly strong indication that Labour would lose and National would win. The confidence in National winning (combined with certainty of Hide winning Epsom) meant that those likely to support ACT came out and ticked ACT, knowing National would comfortably surpass Labour. That was not the case in 2005, when National needed all the votes it could get to try to pass Labour (and ACT's polling was a self fulfilling prophecy). More importantly, those on the left saw Labour as losing, and its only chance being a coalition with the Greens, as a result the Greens did better than in 2005. In 2005 the Greens were almost wiped out as Labour looked neck and neck with National. The Greens will do better with specials, but they haven't done that well, as it would have been comfortable for Labour voters to turn Green given the polls - it suggests the Greens face some brand burnout, paying the price for the recession and the anti-smacking law - both of which should fade a bit in three years.
Another factor is NZ First and United Future, both burnt by being part of the government. Those wanting a change in government saw little point supporting them, those wanting to stick to Labour would vote Labour. Jim Anderton's Progressives continue to shrink, why vote for him instead of Labour?
A neck and neck race decimated small parties, excluding the Maori Party which was new and was occupying a different part of the political demographic. All small parties were hurt as people rallied to the two main parties, the Greens and NZ First scraped in, ACT focused on Epsom to save itself, and United Future was decimated. Why? Because those who voted United Future in 2002 did so to give Labour a coalition partner that was centrist. With National now having a chance of winning, and United Future having propped up Labour in 2002, National was the preference for half of those voters. Notice how Jim Anderton's Progressive shrunk further as it was indistinguishable from Labour.
Pretty much a forgone conclusion for Labour, as a result ACT had its best ever result at 7.14% as National voters gave up, United Future pulled off 6.69% as National voters gave Labour a coalition partner to the right (once Dunne's profile had been lifted by a single TV debate) and NZ First awakened its latent supporters getting 10.38%. The Greens also got 7%, an improvement on 1999. The flipside was the Alliance, which lost badly because it was seen as part of the government, not helped by Jim Anderton going off on his own - you either supported the government (voting Labour) or wanted it moulded in one direction or another (Greens/United Future). However, overall minor parties do well when the result of the majors looks conclusive.
Very high likelihood of Labour victory, so ACT gained over 7% as National voters scrambled for a good coalition partner. By contrast, NZ First was punished by its supporters who wanted a change of government, getting 4.26% (virtually the same as 2008). The effect of being in coalition with the outgoing incumbent government. The Greens were new and novel, and grabbed just over 5%, harming the Alliance a little (7.74% rather than 10% in 1996). However again, with Labour having a fairly sure victory, enough voted Alliance because Labour was seen as comfortable. United at this point was seen as irrelevant and had no profile.
So what does this mean for the future? Well for minor parties, the best comes when the result of the major parties is fairly certain AND you are not part of an outgoing government.
However there is one other point to note - the demise of NZ First, the imminent demise of Jim Anderton's Progressives and United Future in its twilight years will all remove three parties largely based on personalities not principles - this will leave the Greens, ACT and the Maori Party as the core small parties in Parliament, all of which I would suggest are in a far better place to hold onto core supporters than the parties formed of ex. Labour and National MPs.