Slots for saving decks as Malechi suggested would be fine but, if you'll pardon the alliterative pun, finite. I imagine only a certain number of slots could be fit on a screen.
I thought of saving the decks a la Guild Wars and keeping client-side plain text lists. Flash cannot do that without security risks though, right?
So how about similar lists server-side? I don't know what DB is used for ETG but maybe add a table for decks with:
Unique IDs[/li]Player ID (either the unique ID for players or account name, if it is used as the UID?)[/li]Deck Name[/li]Card ID[/li]Card Int (number of specific type of card specified as the Card ID)[/li]Player Owns Card (y/n)[/li]
To look something like:
0500 | seditiousbroom | Ice Deck 5 | freeze | 4 | y
0501 | seditiousbroom | Ice Deck 5 | icebolt | 3 | y
0502 | seditiousbroom | Ice Deck 5 | purify | 1 | y
Then add two buttons on the top left portion of the deck management user interface (Your Deck button). Maybe so the menu looks like:
Load Deck[/li]Save Deck[/li]Remove All[/li]
Not sure about the Player Owns Card (y/n) bit above. How would you limit saved decks to allow only cards a player owns? Using a y/n flag like that would have to be updated every time someone entered the bazaar. To say nothing of tracking how many of a given card a player owns. So that Player Owns Card (y/n) part likely would not cut it.
Any additional ideas? Suggestions for improving? Different stuff altogether?
Also, opfinistic, I would love to see a copy of your spreadsheet or even just the basic layout.