I remember way back in my first term in Oxford (MT 2000) it only took me until my second philosophy tute to be so lost by Moore's naturalistic fallacy that I resorted to looking online - now seemingly the first resort of most undergraduates - and came across an online essay bank. I didn't copy anything, but I did read one essay and include it on my bibliography - the same as any other article I might have read - and my tutor picked up on it.
Today, for the first time, I had clear signs that one of my students may have resorted to plagiarism. He sent in his essay, yet when I printed it I found it had someone else's name and the date (10/10/05) on the top. He'd obviously missed this header, as it was only visible in print layout!
Of course, this doesn't mean he necessarily was plagiarising - his claim was that he'd used the other guy's essay as a 'template' but written "most of it" himself. Nonetheless I have reported the matter to his tutor and senior tutor. I'll leave it to them to investigate and take action, since it's not really my job. (It being only a tutorial essay, rather than assessed work, the matter is less serious. Though for his sake I'm glad he isn't at St Anne's, having heard some horrifying stories about one of their tutors, who takes academic integrity very seriously).
The issue of plagiarism is obviously one that interests academics; I was reminded of this old post on CT.