Anyway: An hour or so ago, I noticed that I had $4.xx worth of Bitcoin sitting in my 21.co account, "earned" in perhaps five minutes of "work" (filling out my profile, answering a couple of questions, agreeing to accept a job offered through the service).
The big question: Could I actually GET that Bitcoin, or was 21.co yet another one of those "earn money online!" scams that disappears when it's time to fork over?
The big answer: Yes, I actually got the Bitcoin (or, rather, the transaction is in the blockchain, although not yet confirmed -- you know how Bitcoin is these days unless you fork over insane miner fees). You can check for yourself -- here's the bulk transaction at BlockCypher. There are four outputs. Mine is the one for 0.002xxxx BTC.
What 21.co sells is the ability to contact people of some claimed expertise/field (and based on my experience, the claims are examined/verified to some degree), either individually or en masse, and actually receive replies. For example, you can contact me through that profile link at the top of the post for a buck. Or you can "Get replies from 33 Andreessen Horowitz partners for $50 per reply." The contact groups are heavy on tech and finance.
Neat idea, in my opinion. Whether or not it will fly, who can say? But I'm already making money with it and kind of hope to continue doing so. What I may do is start offering email consulting in some specific field, with 21.co as the payment collection end of things. You want to talk to me about X, it costs $Y per email (with emails of unreasonable length not being replied to and therefore not being paid for).