Historically, I don't recall any significant sale prices for Macbook Airs on Black Friday. Perhaps something like $50 off. Some might consider that significant, but I don't.
Best Buy has been regularly offering MBA's on sale since the early Summer. Between the sale price and .edu discount (if applicable in your situation) they have been Black Friday "door buster"-like prices (percentage discounts similar to infamous Black Friday "door buster" deals).
One example: I purchased an 11" MBA 4GB/128GB back in June @ Best Buy. Sale price plus .edu discount: $650. with additional discounts/incentives, $450 out-the-door (tax included).
That is a lot of words to say, "If you find a good sale on MBA's before Black Friday, buy it don't wait."