Here's an interesting statistical analyis of deck opening/card crafting: http://iam.yellingontheinternet.com/201 ... arthstone/

The highlights include:
512 decks required on average to attain every card
Most efficient method of attaining cards is to continue opening packs until you have enough dust to craft all remaining cards
Carfting commons and rares is almost always (99% of the time) a dust loss.
The best cards to craft with dust are legendaries
Dust is worth a little of 1g each
Arena is still worthwhile even with win rates such as 1-3 or 2-3