I have a dual screen set up at home, so it is not uncommon for me to be watching a DVD or some other movie/series on my secondary monitor while playing WoW on my primary. As most people know, unless you're PvPing, you can pretty much go on auto-cruise for farming.

I honestly can't say that I've noticed much of a difference with/without media player running so I guess what others have said in this thread is true, it mainly affects older system. /shrug

LOL true.