As opposed to freelancing, crowd sourcing firstly involves multiple people as well as splitting of the tasks between them. Usually these tasks do not require any expert skills; knowledge of the computer/ Internet and/ or a mobile phone are sufficient.
A number of websites have sprung up in the recent years where a business can make use of the "crowd" and the "crowd" can earn money by completing activities such as taking a survey or translating a paragraph of text, etc. Typical earnings can range from $0.01 to $20 for each task completed. Each task should ideally be less than an hour of work.
Following are some sites where "tasks for the crowd" can be posted:
Amazon Mechanical Turk
Amazon Mechanical Turk is a marketplace to find "human intelligence tasks" (HIT) and thus, earn money. Earnings in the US can be transferred to a bank account. Earnings in other countries, however, are redeemable only against Amazon.com gift vouchers.
While backed with Amazon, the site is attracting too much spam; it's said that 40% of the tasks on the crowd sourcing site consist of fraudulent/ spamming activities . Most of the tasks on AMT are related to "liking" something on Facebook or re-tweeting something for someone; all meant to generate "non-genuine" SEO ranking or page views of some website. Still, some people have managed to utilize the site for supporting their research by paying people to participate in surveys.
TxtEagle's concept is to create simple tasks that can be completed using a mobile phone in a developing country, usually via SMS. An example scenario could be translation of an essay from English to a native African language by breaking the article into paragraphs and making each sentence available for translation.
TxtEagle promises to provide Quality, Speed and Security. One measure they have taken, for example, to ensure quality is to compare the response of the "workers" with known results from the data set, and thus, ensuring that they are accurately answering questions.
It's not very clearly laid out how one can register to receive work from TxtEagle. Here is the link to register for TxtEagle.
Cloud Crowd is a Facebook app. They have created a specialized set of services that can be worked on (i.e., the type of work that can be outsourced must be one of the predefined ones). As of now, they allow essay writing, singing songs for a requester, finding URLs', extracting data, promote something, and a few other tasks.
Payment is only by PayPal which is a hard barrier for many people from countries like Pakistan where Paypal doesn't operate.
Service provides offer a service for a day's work from any of the following rates: $8, $16 and $32. Typical service, for example, could be "creation of a business logo in a day for $8." You can post your own services or make use of the ones offered there.
While the concept is very promising, it's hard to say that crowd sourcing is ready for prime time. Yet, existence of the commercial sites indicate that you can utilize the efforts of the crowd where possible. One such application is to filter large amount of data for the purpose of research, specially if your research/ survey is related to the developing world. $0.01 for a survey question's response is not costly.
It's interesting that $1 or less for an hour worth of work doesn't make sense in the US and the Europe, there are not very many ways of getting payments in poorer countries. Paypal, for example, doesn't operate in Pakistan. Amazon's gift certificates do not mean much in Africa, either.
Some Interesting Links
 40% of Amazon Mechanical Turk is Spam!
 Guidelines for using AMT