Love this site, some ideas for your consideration...
Cube Support:
While I can certainly create a new deck and stick a really long deck list in there for a cube, it does lack for a couple of things....
1) It would be nice to have different stats when you look at the statistics to show what packs look like randomly and show you the balance of colors, lands as opposed to assuming this is a deck for personal use
2) Very *minor* annoyance that it calls my vintage "deck" an incomplete EDH deck. Rather than try to infer the type of deck based on the numbers, it would seem better to me to make me tell you what I'm building.
Better TCGPlayer.com integration:
I have to admit that I've not looked at the API specs for TCGPlayer.com to see if this is even possible (i.e. that they have such call you can make), but it would be fantastic to go into a deck / cube and click a single button to populate a cart in tcgplayer for all cards not marked in my inventory. If I'm building a 700 card cube and don't own 300+ of the cards I'm looking for, I *really* don't want to type those by hand
Std Deck Building Enhancement:
As Gatecrash is approaching, I've been building proxy decks to test with at home using spoiled cards to find out what the metagame's shaping up to look like and decide which direction I want to go. Problem of course is that, none of those spoiled cards are in the database so I can't add them to a deck. Two solutions I can think of for this:
1) Add spoiled cards to the database. If you don't want those mucking things up, maybe I have to click a flag somewhere to include them in the search?
2) A more flexible solution might be to allow me to add "generic" cards to a deck...I put in the name and mana cost and a note or something...