Hey foos
we_trust_snape
Another little speculation (HBP spoiler)...
After Slughorn's Christmas Party, Harry overheard Snape telling Malfoy he had made an unbreakable vow, right? So at Harry's next meeting with Dumbledore, he told Dumbledore everything he heard, to which Dumbledore didn't seem to be affected at all. He even said that he "understood more" than Harry did, and that Harry did not tell him anything that caused him disquiet. So... Dumbledore knew about at least part of the vow the whole time...
Just throwing that out there.
Another little speculation (HBP spoiler)...
After Slughorn's Christmas Party, Harry overheard Snape telling Malfoy he had made an unbreakable vow, right? So at Harry's next meeting with Dumbledore, he told Dumbledore everything he heard, to which Dumbledore didn't seem to be affected at all. He even said that he "understood more" than Harry did, and that Harry did not tell him anything that caused him disquiet. So... Dumbledore knew about at least part of the vow the whole time...
Just throwing that out there.