I still have yet to make a penny playing Diablo 3, but I am taking some steps toward investing my small amount of gold into items that I think will be able to sell on the Real Money Auction House. As of right now, the only items that can be sold on the RMAH are equipment items. Given my "industry opposite" schedule of playing the game in the mornings before work (a few hours after the normal gamer has gone to bed), I am trying out an Auction House strategy that I hope will pay some solid dividends and help me achieve my goal of making money playing Diablo 3.
The massive amount of players that are on each "server" allows for a huge amount of drops in the game. There are thousands of Legendary level items showing up on the GAH and RMAH, meaning that some players are willing to let go of their once in a month drops for redonkulously low prices. My strategy is to check the AH for Legendary items (right now I'm just checking for Barbarian items because that is the class that I know the best) and find auctions that have high buy outs but extremely low bids. I've found several items that have buyouts upwards of 500,000 and bids as low as 1,000. Because most players do not play in the mornings, if these auctions are ending in a short amount of time, I will put a bid on them and try to scoop a Legendary item for cheap.
I just started trying out this strategy yesterday and have already won several auctions. I've put a couple items up on the RMAH for low prices (around $5), so we we will see if any of them sell over the next few days. If this strategy works, I will continue to use it for Barbarian legendary items and eventually branch out into other markets as I have time to get to know and play other characters.
Update: I'm slowly climbing the level ladder and dinged 37 last night. I can't wait to get to 60 and start building my MF and GF sets, but I still have a ton of grinding to do. Better get back to it!