I would be really glad to see more operations within a single chosen set. Right now I can't, for instance, even estimate how many cards of a single set I have in my wishlist, unless I count them one by one across all pages while the filter is on. So I'd like to see the number of cards filtered besides the overall number of cards.
I'd love to have "set checklist" option: pre-filled full set sheet to work with. And more to that matter: it might be really easier for the guys with a LOT of cards to add, to work "inverted" - add the whole set to inventory or wherever, and then just uncheck the missing few ones, instead of painstakingly filling all in one by one (and then applying a correct set to every card added, doubling the pain!).
It would be great to have automatic Set applying to a bunch of cards being added through the "multiple import" field. Say, I entered my excel list of Mirrodin cards in the field, and I could have a "Mirrodin Set" attribute applied to all of them at once when I press "Import".
It also would be nice to have the Collector's Number of the card in its set, though I realize it's quite confusing when a single card has a multiple sets as its attribute...
Otherwise I'd like to say that this site is the best card inventory on the Net I found by now, great job, guys! Which means, all of the above is not mere complains but more of a desires 