I think it's a cool idea. I thought about doing a "Patina 2010 Watch" on my blog because that's the shadow that I am soooo close to using up. But I wouldn't go on a No-Buy until I used up 10 products. Perhaps until I hit the pan on 10 products, but not use them up in their entirety. That would take soooo long. But finishing a product does give you such a sense of accomplishment.
Also I've considered this before, and discussed this with my friend and blog partner (because she disagrees), but for me, the point of using a product (especially a color product, rather than a basic face product like foundation, powder, or concealer) isn't to use it up, but just to get good use out of it. I'm never going to use up every product in my collection, nor do I want to. Sure I want to use up liquid and cream products with expiration dates in a timely manner, but I don't want to necessarily run out of eye shadows, blushes, etc. I just want to make sure that I'm getting my moneys worth out of a product, which is ultimately a personal estimation, that for me differs with the nature of the product. For example, I think I'm doing great if I get 5 or more uses out of an eye shadow.
I think something that I'd be more interested in doing is a "Shop Your Stash" Personal Challenge where you have to use half, or a quarter, or perhaps your entire collections worth of products at least once before you allow yourself to buy something new. That would be so cool because I think most of us have a tendency to use our favorite products, or our favorite new product of the moment on a regular basis and kind of forget about all that other stuff at the bottom of the train case. Plus you'd get really creative with color combos.
That to me seems like a more enjoyable way to drive the point home, and you don't have this singular obsession to finish a product, and you don't force yourself into a beauty rut because you're using the same products and colors over and over again.
That was longer than I intended it to be...