The Harper conservatives caused the surge in NDP support. They pushed the coalition argument too hard and failed to address the issues voters feel are important. Happy Jack Layton pushed harder on a range of issues. In Quebec, it was a simple matter of their voters becoming tired of the separatist argument. They became more interested in the issues that matter to them. When Quebec voters pushed back on the other three parties they had only Jack Layton to support.
When the NDP support went up in Quebec both conservatives and liberals made the mistake of launching attack ads against Jack Layton. This only caused his momentum to spread across the country. Influenced by polls the mainstream media placed the Layton NDP at the top of their news reports and added further support for the NDP.
The conservatives pressed too hard on the issue of who was going to govern the country after the election. The voters generally feel one party is as bad as the other is when it comes to governing the country. Harper comes off as if he is the only person whom can govern the country. It seems the voters may not agree and again confine him to a minority government.
When the smoke clears, we may not see the historic changes predicted by the media and polling companies. The voters are having some fun with the politicians this time around. It is an interesting election!