I've heard countless times that "If Bitcoin difficulty gets too high to cover electricity costs, I'll just have 10 good gaming rigs to sell on Craigslist -- problem solved!"
I live in one of the best-off areas on the country, economically. We're practically "missing out" on the Greater Depression (the government and mainstream media call it a "recession", or even a "recession that ended last year" -- yeah right!) And there are PLENTY of people here, too. I'm talking about San Antonio, TX.
I've been following Craigslist, oh, since about when I got into mining.
Let me say this about Gaming Machines.
1. There are LOTS of used Dells on my local CL, usually selling for $50-$100. Often this includes a 17" flatscreen monitor, keyboard, and mouse.
2. I've seen LOTS of systems for $250 or less. $250 seems to be the sweetspot, and almost always includes a monitor (LCD, *not* CRT), keyboard, mouse, and sometimes a desk!
3. Gaming machines are custom by nature. They tend to be built with high-end components (read: depreciate rapidly), and things that add "cool factor" (read: useless and without practical value).
Why would the World's Biggest Gamer ever buy a "used" gaming rig -- ever? For the same price you can go on NewEgg and pick out YOUR dream gaming rig. You can pick your own video card, case, etc.
To make a used system worthwhile, it would have to be at a GOOD PRICE. But the original owner is already losing 50% or more of what he paid. So he'll be reluctant to bring everything down to market value, then LOWER THE PRICE A BIT MORE SO IT'S A GOOD DEAL so someone will actually want to buy it.
Anyhow, my point: Gaming systems -- any system over $250, really -- tend to SIT THERE for weeks on end. And this is in an area with more cash sloshing around than most. We have a lot of military here -- and the Gov't hasn't laid anyone off yet. Certainly not the military!
Oh, and if you're thinking of selling your rigs as gaming rigs AFTER BITCOIN MINING BECOMES UNPROFITABLE, then you're going to have an additional obstacle -- you won't have people clamoring to get into Bitcoin mining. After all, you were all set up (hardware, software, cooling) and decided mining wasn't worth it -- you think someone with 0 experience is going to want to jump in? Get real.
Just more food for thought.
P.S. All the people thinking about selling their systems -- do they have 5 or 10 Windows 7 COA's (Certificate of Authenticity) lying around? You might be able to put pirate versions of Windows on your mining rigs -- or Linux, which is free -- but do you think the average gamer wants to NOT be able to re-install the software on his PC, or use a non-Windows OS?