Check out this chart from Ekos, via Paul Wells. You'll note that, for all the screeching Liberals circa 2004-5 did about the NDP stealing their votes, in this case the NDP is almost entirely innocent: the Liberals have lost many more votes to the Tories, and almost as many votes to the Greens, as they have to the NDP. Kind of makes you wonder why the Liberals have helped out the Greens as much as they have.
(Some have objected to this contention, for reasons that elude me: the Liberals, since shortly before Dion was elected, have trumpeted their friendship with the Green party, and helped raise the party's national standing.)
Some basic questions here: How progressive is the Liberal Party? We saw in 2006 that the (non-Conservative) party most comfortable with the prospect of a Stephen Harper majority is... the Liberals. Now we see defecting Liberals as the single biggest source of vote-crossers for the Conservative party.
To answer my own question: the Liberal Party is getting more and more progressive by the day, apparently. As it becomes less blue and more red, the party can't help but be more progressive. Whether it can win an election at the same time remains to be seen.