As I have argued previously, of the three parties with a presence in the ROC, GST/PST harmonization as an issue in any upcoming federal election probably works to the advantage of the NDP, with both the LPoC and CPoC suffering a bit because of their association, on either the federal or provincial level, with the process. So if Harper is willing to trade a little weakness on his own squad for a stronger NDP and a Liberal party that is weaker still, this would be a smart move tactically.
I would therefore suggest that the Libs think of a way to support such legislation, especially if (as the article referenced above would suggest) it is introduced as a stand-alone bill. There are a couple of justifications for this stance (other than the ones that involve the stench of terror).
1) The policy Ignatieff has settled upon is to do nothing to hinder any federal/provincial harmonization deal, and although this position was taken hypothetically and dependent upon the existence of an Ignatieff-led Liberal government, I see no particular reason there should be a different position as opposition. Why get in the way of a deal struck by the (quite popular) McGuinty Liberals?
2) I find that this "voting blindly against" allegation sticks in the craw a little bit. It seemed silly of the NDP to take a stand against every little piece of legislation without even having seen it, and now the Libs risk getting stuck in the same situation. Given that Thursdays' non-confidence motion will fail, if this legislation comes forward between now and the next opposition stay and, as a stand-alone, is acceptable, then it should be supported.
Of course who knows what the Bloc will do? They don't have a stake in this game policy-wise, having harmonized their sales tax years ago. Tactically, given CROP's latest result, I would think they'd be inclined to support.