Paul Wells has a good catch - comparing the results of different polls in a seat projector. Turns out, more NDP votes gives the NDP more seats. Screwy, no? The way the Grits have written the script, a vote for the NDP is a vote for Harper. Turns out, a vote for the NDP is a vote for... the NDP. In fact, it seems like the only surefire way to keep Harper in minority territory at this point is to vote NDP. This actually makes sense - there's a bunch of seats (Ontario and BC, I'd imagine) where the NDP and the Tories are the only ones in the running, or where it's a tight three-way race. Voting Liberal won't tip the scales in the Tory/NDP races, and will only rescue a few of the tight 3-way races.
So, progressives: Vote NDP. It's the only choice.