Have a lot of NDP voters switched to LIB for tactical purposes?
Yes!! Yes!! Yes!!
In general, the NDP ran a campaign as if they were already in government, running for re-election, and had a wide lead in the polls. They then moved to the centre to try to win a majority. This allowed the Liberals to campaign on their left.
In any case, the polls had shown for years that Liberal and NDP supporters are open to supporting the other party. And this is Canada, where political tribalism is nowhere as deep as in the US or Britain.
Then, Harper's Muslim-bashing caused a sizeable bump in his support by galvanizing his base. Unfortunately for him it also galvanized his opponents into supporting the only party capable of beating him. In the final weeks, the NDP's clearly desperate tactics (like claiming they only need 35 more seats to defeat Harper 
) only furthered this stampede.
Well, elections with 3 or more parties or candidates of roughly the same strength tend to have strategic voting causing interesting swings that the 2 party US system isn't going to produce. The 1993 Canadian election is really unbelievable from an American perspective.
