I have seen a draw bug twice, the card flips across the screen like normal, then does not show up in my hand. The first time it happened i got more cards in my hand after a few turns, and the game made me discard even though it only showed 7 cards in my hand. Not sure if this bug is arena specific, but I have only seen it in the arena.
Also, and this may not be a bug at all, I played my own arena deck in Gold, lost (not intentionally, i want rare spins more then 5 gp or ranking), but my deck's number of games did not increase, i was 1-0 before i played myself, and 1-0 after i played myself.
using OS X 10.4.11, Firefox 3.6.18