If you're in the habit of sharing your headphones a lot with friends and family members, the Sharebuds are an intriguing concept--but the retractable-cord design isn't implemented as well as it could be and the headphones are overpriced.
If you're constantly sharing your earbuds with friends or family members, Mida Interactive has a better solution than just listening to mono out of one earbud: the ShareBuds Twin MX Earphones with a retractable cable.
The company accomplishes this by offering a single plug that breaks into a Y early on for the two earphones; then, two retractable spools offer two more cables apiece that split into individual pairs of earbuds.
The retractable design helps prevent the cables from becoming tangled, but the spool mechanism doesn't work all that well in this case. It will still take some effort on your part to keep things unwinding properly.