Why there was a market for burnt-out light bulbs in the former USSR:

For most of us, it is hard to fathom the rationale for a market in burnt-out light bulbs. But in the scarcity-driven Soviet economy, the market was entirely reasonable. Light bulbs were rarely available to individual consumers, but were obtainable for state-sponsored activities.

Thus, it would be difficult to purchase a light bulb for a new lamp in one's home, while burnt-out bulbs in state-run offices or factories were routinely replaced. So if someone purchased a new lamp and needed a bulb, he would buy a used light bulb for a small fee and replace a functioning bulb at work with the dud. He would then take the functioning bulb home for the new lamp, while the burnt-out bulb at the office/factory would be replaced with a new functioning bulb.

Meanwhile, the maintenance person at the office/factory would take the used bulb and sell it on the used light bulb market...

(Via Marginal Revolution.)