I think this was from a long time ago... but I'd love this feature as well. I want to offer a day where someone can choose one product from 15 various products and get a sizable discount... but only be able to use that discount once on the site. If I try to discount this group of products now individually, would the customer be able to apply the discount to all of the products, or can I limit each customer to one use of the same code. Man... it's even confusing to type this. Maybe I know now why it's not a feature yet.
Anyway... summing up. One discount spread across multiple products, single use. Feature request and thanks for reading my ramble.