I'm speculating a bit here, but in the last couple of weeks, Jack Layton and Stephen Harper meet, and then this week, NDP Premier Gary Doer is appointed Canada's next ambassador to Washington.
To say that the timing of this is a little fishy is an understatement, but it fits. Layton has very carefully avoided actually criticizing the Harper government directly - instead choosing to frame his criticism of Harper's recent round of pork barrel patronage in terms of the Liberals:
"He has declared to the Canadian public that he would not name unelected people to the Senate. ... His word means less and less every day he's in office, and he's behaving more and more like the Liberals," NDP Leader Jack Layton said of Harper.
One has to wonder about the NDP's soft-pedalling of its criticisms of the Harper government when suddenly one of the NDP's longest serving public figures is granted a plum appointment by Canada's most partisan Prime Minister. Harper doesn't typically do things like this unless he's getting something out of it.
In this case, he gets to point to Doer as an example where he has apparently not been partisan, and I suspect that he also gets Layton to be somewhat passive for the next few months - and Layton will continue to focus his efforts on the Liberals instead of the government.
Layton will, of course, continue to talk vaguely in terms of "fundamental differences" with the Conservatives and it will be a rare vote that he actually aligns with the Conservatives in the House of Commons. He holds enough of a weight in the House of Commons that he can order his caucus to vote against the government, and thereby act as a fulcrum for whatever lever Harper is trying to apply to the Liberals.
Layton knows that an election right now will go against him, and likely as not end his political career - party leaders that lose seats tend not to survive so very long...even in the NDP.