What do Bitcoin, angel investors, and high-school algebra have in common? Before I answer that question, I need to tell a story.
Bitcoin
In 1995, I lived in Washington, D.C. At the time, Citibank was in the process of replacing its monochrome ASCII-only ATMs with spiffy new color bit-map machines. We users had to adjust to the new interface, including the conversational tone of the new software. For example, instead of offering buttons labeled “Checking” and “Savings”, the machine would politely ask “From what account do you wish do withdraw money?” And, while checking to see whether you had enough money in your account, the ATM would let you know it hadn’t forgotten you by saying “I’m working on it.”
Hilarity ensued one day while I was in line for the ATM. The man in front of me was clearly in a hurry. He requested his cash and shouted “Hurry up!” at the ATM. The machine responded “I’m working on it.” He interpreted the message not as a sincere expression of its desire to perform the requested task, but rather as a defensive response to his “Hurry up!”, and proceeded to harangue the machine as to how it should address valued customers.
The user interface mistake made by Citibank was that there was no progress bar. In other words, there was no proof the machine really was working.
Which brings us to Bitcoin.
Bitcoin is, of course, all the rage these days. Usually referred to as a virtual currency, people and businesses can exchange bitcoins in much the same way that they exchange United States Dollars, or any other currency. Spending bitcoin isn’t conceptually different from writing a check; if you have bitcoin, you can transfer it to someone else by (cryptographically) signing a message that says to whom you wish to make the transfer. But, unlike other currencies, new bitcoins don’t come from a central bank.
Instead, new bitcoins are created through hard work. If you want to get yourself a new bitcoin, all you have to do is be the first person to solve a math problem. But, these math problems are hard because the only known way to solve them is “guess-and-check”; you have to randomly try possible answers until you find the right one. And, since there are zillions of possible answers, you need a fast computer, and a lot of electricity, to find a solution. So, if you’ve solved the problem, you have — unless you got very lucky — done a lot of work. Thus, a bitcoin is “proof of work.”
In a recent post, I mentioned that I had joined the Sand Hill Angels, an angel-investor group in Silicon Valley. I expected that the process for joining would entail filling in a form or two and then signing a legal agreement. But, it turns out that SHA isn’t just looking for people who have the financial means to invest in start-ups. And, in fact, it is actively trying to screen out people who want to sell services to the other members, or who just want an inside track on what’s going on in Silicon Valley. Instead, SHA wants members who are attend meetings regularly, make regular investments, bring in candidate companies, assist in due diligence, assist portfolio companies post-investment, and help with the administration of the group. In other words, while SHA certainly doesn’t expect that its members are full-time investors, it does expect that angel investing is one of the hobbies to which they are most committed.
So, new potential members are expected to attend several meetings and meet with existing members to discuss what they hope to contribute to and receive from the group. There is also a step (which I will not disclose) that is a non-obvious test of business acumen and interest. In other words, joining the group requires “proof of work,” not just signing a piece of paper.
Of course, as school children, we were often encouraged to “show our work” when doing math problems. Even if we didn’t get the answer right, we might sometimes get partial credit for using the right method, or for getting some of the steps right. And, showing our work was (circumstantial) evidence that we hadn’t copied from someone else. In that sense, showing the steps required to solve the problem was “proof of work.”
I’m not sure that there’s a business idea in here, but there are undoubtedly other circumstances under which proving that work has been done is likely to be valuable. Warehouse staff prove that they’re working every time they ship a box. But, lawyers, accountants and consultants often have no firm proof of work when they bill their hours. What if they could prove they’d been working, and working smart? Or, what it when a flight was delayed, the airline could prove it was working hard to get you where you were going as soon as possible?
I’m pretty sure that would be better than a gate agent saying “I’m working on it!”
Keeping Busy 
The genius of github is (in part) that by pushing a set of commits, a developer shows that he/she is “working on it.” What I’ve been mulling over of late is how we can re-employ the legion of long-term unemployed in the Rust Belt. We have scads of hard-working people who have no skills relevant to the new economy. Part of the answer of how we can match them with work is how they prove they’ve done something remotely. Update newsletters from Kickstarter and its competitors are another progress update mechanism. Assuredly the combination of cryptographic signing and transmission by a virtual escrow system are important. EBay and AirBnB use these mechanims, too.
Yes, GitHub is another good example. I recently learned of a two-day programming contest that used GitHub to “prove” that the work turned in by the teams was not begun before the contest started; you had to create a new GitHub repository as Step #1 of the contest, and then do all your work there. Of course, you could have copied in work from elsewhere, but it would be hard to factor it into little git commits and such, so this mechanism is certainly a proof-of-work.
Another example of proof-of-work is a college education. Many of the things we learn in college aren’t necessarily terribly useful, but obtaining a college degree has traditionally been a way of convincing employers that (a) you were reasonably smart (or you wouldn’t have gotten into college), and (b) you knew how to work (or you wouldn’t have gotten out).
So, for your example of people who need new skills, perhaps the question is what you want to demonstrate. Perhaps it’s not skill per se, but instead the meta-ability to learn a new skill — and the willingness to do the work necessary. If these folks can exhibit an appropriate proof-of-work, you might be more willing to invest in the additional training required for whatever skill you want.