The following data is from Link Building Seminar, Scaling White H by Will Critchlow in 2011. The rough number of articles published to gain an addition link from a new domain:
- Cracked.com : 2 articles
- Wikipedia.com: 4 articles
- BBC: 12 articles
- Nytimes.com : 17 articles
- Mahalo.com: 30 articles
- Ehow.com: 50 articles
- Youtube.com: 100 videos
- Faceboo.com 400 new users
- Amazon.com: 500 products
- Answers.yahoo.com: 900 new posts
High quality articles are more likely to generate links the poor quality articles. Other factors also have an effect like humour.
Hope this gives you some ideas, on what is required to produce a link.