What happens if one spouse has filed their taxes and the other has not? Do you still get the family HST rebate cheque?
This is an interesting question. I couldn't find definitive information on it, so your best bet for a certain answer is to call the Canada Revenue Agency at 1 877 627-6645.
However, here's my thinking on the subject:
As a couple, it's possible to receive no HST rebate benefit if family net income exceeds $166,700. Refer to the "phase out range" in the table at this other question.
If Canada Revenue Agency only has one of the two tax returns needed for a couple, (and presumably they know they're dealing with a couple based on previous filings or the one current filing), then how are they to know if the couple qualifies or not? The second tax return could, in theory, place the couple's combined net income over the threshold!
Therefore: I would assume that if CRA is missing half of the story, they would not send any HST transition cheque at all, since there's a chance the spouse's missing income could totally disqualify the couple from any benefits.
While that seems logical to me, I can't confirm that's how it actually works.
But there's some good news: late filers can still qualify for a benefit. Refer to: Ontario Sales Tax Transition Benefit: Can you still get first cheque even if 2009 taxes are filed later?