Basically this would be like creating a deck, except cards put in a list arent counted as being in a built deck or deck idea. This could be useful for creating reference lists or maybe noting the location of cards in binders or boxes. It's a simple idea that could be really helpful for collection tracking.

Cool! +1 to this idea.

My use case is simple:
1. I ordered cards from Card Kingdom or TCG - I want to add the to the separate list.
2. I want to have an option (opt in/out) to treat as though they are in my inventory.
3. Once cards are received - I want to move cards to my inventory and delete the list.

Also couple of nice options to add once custom lists are there:
1. Provide integration with eBay so we can see what cards we are bidding/purchased with the option to move them to our inventory.
2. Provide API to allow custom integration with whatever site user wants.