(Thanks for sending me a heads-up. Not that I wouldn't have seen this on my own, as I check the forums daily, but it was very thoughtful of you and I feel special!)
I think that this method was exactly what I had in mind. Applying it to wishlists is just icing on the cake. If you are new to this forum, or don't fully grasp what is being attempted here, keep reading.
I have a collection of many thousands of cards. Maybe even tens of thousands. While inventorying this entire collection sounds like a smart thing to do, it turns out that when I go to find a card that I have one copy of, I spend just as much time as I would have without the inventory to find it among all the boxes and binders of cards. Or worse yet, I go on a mad hunt trying to find this card and it turns out that I mistakenly added it to the inventory without actually owning it.
The labels function being proposed allows me to add cards to the inventory, for the purpose of building a tradelist or otherwise, but then also keeps the virtual collection of cards separated by the appropriate real-world box/binder. Example:
I decide that I am going to build a mono-green Rofellos EDH deck. I know I need a Priest of Titania card for this deck, but I'm unsure of where I keep my two copies. In the past, I had to search every green box of cards I owned, plus my vintage binder, plus my trade binder, and my EDH binder two find one of the two copies I own. Fast foward to the future, where all my boxes and binders are appropriately inventoried, and I am able to see at a glance that there is one copy in my EDH Binder, and another in my box of vintage green. I have halved my search time, and found the one that wasn't in a binder (and found out it's a $4.00 common!).