I see it as a good way to earn some extra pocket money, as another commenter said, "for the ride home."
Even those who don't have time to contract will generally have more productive outlets available (... which is often how they became experts).
I'd rather have one $1000 transaction than a dozen $100 transactions unless the process was completely automated (no one questioning time-tracking, no getting-to-know-you period, no trading contact details - just work done and money in the account).
We reduced the max shift from 2 hours to 1. We think this stresses that this is more of a tool to get small things done, meet future potential clients/employees, and earn small amounts of cash now versus a way to make a living.
Basically, instead of spending 17 hours looking for work, we think it makes more sense to do small <1 hr jobs for 17 people. That's 17 new potential future clients(at your regular rate). and it's ~$70-$150 bucks in your pocket(depending if they are 30 min or 1hr jobs). And you helped 17 people!
Does that sound like something you'd want?
Plus I regularly hire freelancers and while making it simply into a freelancer market place would be a horrible idea, I would definitely say that I would hire someone who has been able to help me out with a problem in 30 mins. And I think it's also a good way for developers to see if their potential clients are complete idiots or if they're not too bad themselves.
Of course this is not an absolute rule, yes yes, it is possible, I just don't see how that really is one core benefit worthy of marketing.
At my usual $150 hour rate, it would take 17 hours on WageMachine to match one hour of work. I could just as easily spend those 17 hours finding that one hour of work (and it wouldn't be just one hour).
[Edit] Thinking about it more, I think your idea is very good, but lacks any real traction without being able to genuinely pay real experts -- I don't mean "highly talented, industrious, college educated, English speaking, and lives in the United States", but rather, someone who has at least a decade of work experience, is near the forefront of their field, and would like to invest some time in assisting, teaching, solving other people's once-off issues.
One of the primary reasons I don't participate in StackOverflow is that the vast majority of questions are simply boring. For $150, nobody is going to ask a boring question (and if they do, at least they're paying market rate for the answer).