I am a high school English teacher and one of my main problems with plagiarism is not with online materials, but with older former students passing assignments to younger current students.
I want to start using the Assignments "activity" to have students turn in papers as a way of keeping old assignments, but I only want it if it can search the documents that have been turned in. That way, if I see something fishy about a student paper, I can do a quick search of past years to see if it's an earlier student's work. If it can't search assignments, I am going to have them submit it (and attach it) in a Discussion Forum, which is searchable.
Or is there another way of doing this? I guess I could do something with Google Docs.