Being both a M:tG nerd AND a software nerd I see a use case for deck versioning and a diff tool. Here's what I had in mind:

[u]Versioning[/u] - Just something simple. Each deck would still be its own set but instead of making a new deck with the exact same name (or the same name plus a "v1.1" at the end) Deckbox would force the deck to have the same name and then add a "v1.1" to the end for me. The existing deck would need a "Create new version" button that copied itself under *almost* the same name but incremented the version number (so v1.1 turn into v1.2 and v1.9 turns into v2.0, etc.) Lastly, the most recent version would be the one visible in my deck list and older versions would be accessibly through some other means so that the decklist doesn't get cluttered.

[u]Diff Tool[/u] - The ability to compare two decks to each other and have the differences automatically highlighted in some way. For example, I want to see what's different between my version of B/W Tokens and my friends; or I want to see what I changed from version 1.0 of my deck to version 1.1. Either way, I would need the ability to select two decks and then get back a view of what's different. The ultimate display is up to you but most I've seen look similar to ,but nicer than, my crude outline below.

Creatures 9 Creatures 10
------------------ ------------------
4 Slag Fiend 3 Slag Fiend
4 Galvanoth 4 Galvanoth
1 Lightning Crafter 3 Lightning Crafter

Depending on my schedule and how long this sits on the "maybe" list I *might* tackle the diff tool on my own and just give it to you because I am a really nice guy. I know I'm super busy for at least the next 2-4 months.

These are both great ideas, and versioning or history is something we definitely want to do. This summer at some point, after the long delayed may release :)