Say I have a mturk task such as follows:
1) Find a website about lawn chairs.
2) Send me the URL.
And I want 500 mturkers to work on this. How do I ensure that they give me unique URLs that no one else has submitted?
Is there some easy way to accomplish this?
You'll probably need some kind of database back-end to keep track of the submissions and either show them to workers.
However, a messy but probably effective strategy would be to send them to an Etherpad page w/ instructions not to provide duplicates. You'll probably have trouble getting later arrivals to take up the task, as your task will get more difficult.
You'll definitely need some way of tracking the created list. If you want to take the dive and learn Rails, take a look at my Turkee gem (http://github.com/aantix/turkee)and the example, Turkee-Iterator (http://github.com/aantix/Turkee-Iterator) as it allows for user submissions (e.g. list items).