I wanted to see if I could make an appreciable amount of money by playing the game whether through actual grinding of content or auction house flipping. To start things off I bought the game using money from selling a bunch of MTGO tickets. For those who don't play MTGO, tickets are sort of an unofficial in-game currency. You normally obtain them by buying them from the MTGO store but if you speculate on card values well, you can actually gain tickets which I did rather successfully (an aside, when I figured this out I financed an entire year's worth of drafts and online release tournaments with an initial investment of something like $20).
My first goal was to see if I could get the game to pay for itself. Surprisingly this didn't take as long as I thought it would. I think within a month I had paid for Diablo 3 with Diablo 3. After that initial goal was reached I didn't have any other goals set so I just set about making money and using it to finance other hobbies. I bought a bunch of games off of Steam, I built my MTG Cube using Diablo 3 funds and I bought a bunch of skins for the champions I use regularly on League of Legends. I was considering buying some Warhammer but that was around the time I came to the conclusion that Warhammer wasn't worth spending money on and instead went and bought more LoL skins. This was about 3 or 4 months after the game broke even and then we ended up moving to a new house.
The house came equipped with a fairly large dining room but we needed a table so it became my goal to raise enough money to get a nice table and chairs for the dining room. This was around Christmas time and Diablo 3 sales were quite good so I was able to raise the money for the table in about 4 weeks, though it took much longer to raise the money for the chairs (I think a few months, but to be fair I wasn't as committed to selling in those months as I had been around Christmas). Altogether the table and chairs cost around $700+.
Now I suppose it might have been easier to just get a second job as minimum wage work pays more than playing Diablo 3 on an hourly basis. However, think of it this way, I generally spend around 15-30 minutes a night playing Diablo 3, I don't have to drive anywhere, it doesn't take much effort (some of the initial research can though) and I can usually do my auction house surfing when I take a break from marking papers. Pretty easy gig even if it pays less than minimum wage.
Anyways, I think my experiment succeeded as I was able to actually get a substantial amount of stuff from the sale of virtual goods. My next goal is to raise enough money by the fall to get a new set of winter tires for my car as I do a lot of driving (the school I work at is actually about 100km away from where I live).