This is, perhaps, something I've missed, but would be incredibly useful and time saving for me at least.

Have all official pre-con decks on the site similar to editions. Then an option to "add deck" to the inventory. This way, when someone buys a pre-con deck (duel decks, the commander 2014 decks, etc) they can simply add the entire deck to their inventory and be done rather than adding individual cards. Because they are official pre-cons, the editions will even be known, so it saves a lot of time.

Yep, this has been requested.

Not quite. Perhaps I chose bad examples. I see and understand the set functionality, but what I'm looking for is a pre-con deck functionality. Let me choose a different example. Lets say I went to the store and bought: DRAGONS OF TARKIR EVENT DECK http://magic.wizards.com/en/articles/archive/feature/dragons-tarkir-event-deck-2015-03-18 This is a pre-con deck. The cards, number of cards, and editions of cards will always be the same. I want to be able to search for this deck, then hit "I own it" and have all the cards in that deck added to my inventory.

Yep, completely agree. Had this on my list, just didn't have time to get to it yet. But I'm getting there :)

Awesome, thanks.

I was looking at adding this as an option in the Edition Checklist screen today.

One question I have is if anyone knows if the printings are exactly the same in all packs for cards with multiple printings.

For example, for Zendikar vs Eldrazi, there are 3 different printings for each land. Is the number of cards with each printing known / the same for all packs?

Honestly, there's already a way of informally doing this: You can just make a list of cards to be added using the "Add Cards From a Text List" option. Anyone could post a text list for a given set as a community service.