Hi Ken,
Here's one I did last year. It wasn't a 72 hour promotion, but I'm still pretty happy with the outcome.
I have a marketing book I wrote that I sell as a physical product to massage therapists. Borrowing an idea from Dan Kennedy, I offer a standard and an order page upsell for a deluxe version. Most buyers go for the more expensive deluxe version.
About 2 weeks before Christmas, I ran an email promotion where if they bought the standard version, I'd upgrade them to the deluxe version, free of charge. I made the sale good until 12 midnight Christmas Eve.
I did a follow-up email 24 hours before the sale ended.
Final result? An 800% increase over my normal monthly sales for that product.
It was a very, very Merry Christmas in my household.
Mike