Tested on:
Win7 Ultimate with latest updates.
Screen resolution: 1680 * 1050
*required fields at creating account not determineable
*no horizontal scrolbar @ edit decks
*Edit Decks: Current Deck: when clicking an added card, the infos(card ID, Card name, quantity, max quantity) in the table is not visible.
*Edit Decks: Current Deck: missing horizontal scrolbar
Get Cards: "Connecting...", user should know if it's working or not. 3progressively blinking points ("." ".." "..." "." ".." ...) would be good.
After Clicking "Get Cards" and game is "connecting" I clicked on "Edit Decks" and there were no cards listed anymore.
After restarting, I was able to see my cards again.
Ideas:
Important:
1-2prebuild decks.
The possibility to build the decks oneself is very good and probably one of the most important for such a game.
For a beginner, like me, it's very much effort to read through all the cards and find out which fit together.
Less important:
Edit Decks: Cards: Shortcuts for moving cards to the deck / from the deck(for example <enter> for adding, <backspace> for removing,
<tab> for switching throug cards and deck. So one can still move through the cards, add them fast and can switch between cards and deck)
Very very lesses:
Graphics.
Not the once from the cards, some are very good, some are...provisional.
But the graphics of the interface. It's a much too common one. Doesn't add atmosphere.
But as said, imo the very most less thing to do, since this is early beta

I will keep an eye on your project, since I like such games(Magic <3).
Another idea: Video Tutorial of how to play, or a tutorial as Magic: TG has it on PS3(if you own one, or have a friend,
download the demo version, the tutorial is included).
Keep the work up
