The Zooniverse team has had amazing success with the OldWeather project to crowdsource coding of old ships logs to extract climate data. And I believe Sunlight did some crowdsourcing (with Mechanical Turk?) to build the Political Party Time database. Are there other services, libraries, etc., that can be used to support crowdsourced volunteers in performing similar types of tasks in open data applications?
I'm imagining tasks like checking a certain percentage of scraped data against the original source, or doing data entry when some documents are in non-machine-readable PDFs. At a minimum I'm assuming a library or service would be able to deal with the user registration and management, setting up task overlap for accuracy checking and user scoring, etc.