It would be useful to be able to take two users' wishlists and tradelists and see the overlap.

I think what you're looking for may be the tables that appear if you go to a user's profile page, under "Trading opportunities". Try this: http://deckbox.org/users/smallshake .

I don't have anything in my Tradelist, so you should only see the intersection of your Tradelist with my Wishlist. Although I just learned that you can switch to using Inventory instead of Tradelist.

Quite a nice collection btw.

Ah, I see it now. And comparing against someone's inventory is good too. I also hadn't noticed that you could go to the specific card pages and see people who have/want that card from there. That makes finding potential trades much easier than hunting through users' profiles.