I'd be surprised if Paypal (or the people likely to kill them) aren't secretly chewing on this as we speak.
Which is to say that it will fly in the face of the general trend of development of these things, which has been towards fewer currencies, not more. More currencies means more friction in trade and commerce, since it makes price comparisons harder and forces buyer and seller to constantly be making conversions; this in turn means less commerce happens, which makes everyone poorer. That's a bad thing, not a good thing.
Either that or you keep all your coins sitting in said exchange so you can instantaneously convert them and pay out. And then lose them all permanently when the exchange has a security flaw.
Currency of the future.
Why can't people (on this site of all places) spend just a little bit of time thinking about how things could work well instead of merely pointing out problems?
Getting paid for a good or service with USD is useful because you can spend it to cover your expenses. If Overstock made OverstockCoins instead of accepting bitcoins, how do they pay their suppliers?
I guess that's more or less what Ars is doing, but I don't see how it makes any sense.
Target is one entity, who trusts themselves. A private ledger works just fine for their gift cards.
Also, people have an incentive to concentrate on the strongest currency. The one with the most mining is most secure against 51% attacks, and the one with the most users is most useful.
Do you mean: A. an attack by the rest of the earth's computing power (e.g. you try to have miners control 51% of the earth's computing power - highly doubtful) or B. an attack by colluding mining pools?
It seems like the B (collusion) attack is simply a matter of the number of pools which have to collude, and not actually related to the absolute value of CPU power. And for A, I'm struggling to see how much [non-colluded] miner power you'd need to fight off an external attack.