How profitable is WoW?

I'm curious to know, just how profitable is World of Warcraft (WoW) for both the game developers and the players? Do the in-game economies and transactions contribute significantly to the overall profitability of the game? And for players, can they actually make a substantial amount of money by trading virtual goods or participating in the game's economy? Is WoW a viable source of income, or is it more of a leisure activity with minimal financial returns?