Something should be done about that ad. I also have a mac pro and the same thing happens. It causes my computer to lock up, overheat, and beach ball.
I couldn't see what my temp was, but the CPU usage shot up very high with that banner ad. I'm using windows xp, and some type of AMD dual core.
14% load is normal for internet browsing, but that AD is abmormal. My computer CPU does not get to 70% even while running video convertation or SETI computations..