Social sites (like facebook, twitter, google plus, yahoo mail, etc) want human beings. To ensure that human beings are there, they use CAPTCHAs. Since all that effort to determine squiggly letters was kind of being wasted, Luis von Ahn, figured it would be great to have people try to figure out words from scanned books that computers couldn't figure out, and thus ReCAPTCHA was born.
Of course, there are bad guys. These folks want to use social sites (like facebook, twitter, google plus, yahoo mail, etc. to send you a free ipad for filling out endless surveys that end in your checking account being emptied as you unbox your very own 241mm x 186mm slab of plywood. Since CAPTCHAs are hard for computers to figure out, they pay folks to guess CAPTCHAs for them. Thousands of them per day.
So, in some respects, the greater force for aiding in the digitizing of lost texts is probably some guy in a coffee shop being paid $.05 for every ten ReCAPTCHAs. Those endless ads for discount Canadian Viagra may have also helped immortalize Robert Guillaume's groundbreaking show.. Or Anne of Green Gables. Maybe we'll go with Anne of Green Gables.
That's fine and dandy for doing distributed OCR work, but what about the other big problems out there?
How about solving a little protein folding? How about matching chromosome sequences? Maybe record weather patterns from historical logs? Sites know "problem nets" and could simple toggle a switch to use the new system. Heck, folks from other countries might actually appreciate not having to deal with figuring out English words.
As long as spammers are paying keyboard monkeys, let's use the spammer's money to help society more than they're trying to ruin it.