I have recently been asked to do some work as a plagiarism consultant for one course. This involves checking the Turnitin and Copycatch results for the module.
Turnitin compares assignments with published work, websites and blogs etc. There are quite a few assignments that came up with relatively high scores on the Turnitin site but when I looked at them, this was mainly due to including source texts in an appendix so these are not considered plagiarism.
Copycatch compares assignments with other assignments. Again, there were some assignments highlighted but the matches were largely due to similar collocations and technical terms. Of course, those that had source texts in the appendix also matched each other but this could be dismissed as a false positive.
So, my first impression is that the risk of plagiarism is taken seriously but the scale of it is quite small on my course.