More and more sites have started to "take advantage" of flash ads nowadays. Most of this is just a nuisance, and the carbon footprint of such ads globally must be tremendous! They take CPU cycles even if on background browser windows, or unseen tabs.
I've been increasingly fed up with them, lately. Luckily there is a very nice solution for Safari: ClickToFlash . I took the version 1.5b4 and it seems to be working fine. My good old laptop (PowerBook G4) is now snappier and way cooler on the laps. I hope.