Here is why I hate TurnItIn
If starters, if you're not familiar with the service, here is a good writeup. Anyways, my issue with the company comes from how they operate. From their own terms comes this gem:
ETS License to use Papers Submitted With regard to papers submitted to the Site, You hereby grant ETS a non-exclusive, royalty-free, perpetual, world-wide, irrevocable license to reproduce, transmit, display, disclose, archive and otherwise use any such papers You submit to the Site, and any resulting feedback or Scoring Service results in connection with ETS's research and development of business and services/products. ETS will not retain any personally identifiable information that may be associated with the papers. This license shall survive the termination of the User Agreement. Any cessation of use of the Site shall not result in the termination of any license You grant herein to ETS. Nothing herein shall preclude ETS from using information independently created by ETS.
Basically, by using their service, you are allowing them to keep and to use your work. No big deal, right? Wrong! They are making money off of my original work. By adding my paper to their database they are adding value to their company. What do I get in return? Jack sh*t. I can't even opt out and I am required to use this to submit papers.
In other words, a company that is supposed to detect plagiarism is stealing student work. And on what scale? Well their website says "100,000+ papers submitted daily by students." That seems like a lot to me.