I've been signed-up for the beta for a while now. I still haven't received my invitation yet.
It's a great idea - and of course it won't be the success reCaptcha was - reCaptcha has the benefit of tens of millions of daily users ('workers') with an unlimited amount of work that needs doing - thanks to automated book-scanning.
With language-learning it's different - both the number of workers and the amount of work that needs doing is substantially smaller, and besides people seem happy with products like Rosetta Stone and language tapes which work when you're not at a computer.
He's got an uphill battle.