I think both from a partisan perspective, and a non-partisan perspective, Iggy is making the right call in moving some amendments for the budget. No, the budget isn't perfect, it isn't even that great, but it is probably the best budget we could expect from Harper at this point. I see that Layton has already started attacking the Liberals again, which is to be expected. Considering that the threat of the coalition was needed to knock Harper down a few pegs, and put forward a budget that is at least not terrible, in theory, the NDP would be content with having indirectly actually played a role in influencing government policy.
But that is not the NDP under Jack Layton. Under his leadership, the NDP has seen an increase in seat count and a decent increase in voter support, (although for all the NDP's talk of an upcoming Orange Revolution, fewer people actually were inspired to cast a vote for the NDP in 2008 then in 2006, as it was for every part save the Greens) but this has been in exchange for increasing irrelevance in parliament itself. The NDP likes to talk about being the "effective opposition", and Layton is once again brought out this talking point, but in reality, the NDP has rarely been less of an influence on policy then it has been since 2006. The NDP helped kill the Paul Martin government's work on the environment, child-care, and Kelowna, and what actual tangible results, from a social democratic perspective, has it gotten out of the Harper government?
Ignatieff correctly recognizes that Canadians want neither another election, or the coalition to take power (an oft overlooked fact is that their is no evidence that the Gov. Gen. would actually allow the coalition to take power, and not just allow Harper to call another needless election). While Jack Layton has turned the NDP into the parliamentary version of Dr. No, voting against anything, Ignatieff has now both trumped him and broken Dion's morale lowering chain of abstentions, by actually getting something extra from Harper, for the benefit of the Canadian people.
I would say actually getting results rather then just standing up when it is time to vote no is being the effective opposition. Also interesting, Ignatieff has made no statement saying that the coalition is dead, Layton is the one who declared that, and then attacked Ignatieff for daring to actually try and craft some bi-partisanship and get results. Co-operation if necessary, but not necessarily co-operation seems to be the NDP's motto. Improvement over left, best, and last I guess, although as long as the Layton NDP fails to actual deliever any positive policy results for those who voted for it, it will still remain an accurate summary of the results of the party.