I have always used Flip4Mac to watch WMV files through Quicktime while using Safari. I have noticed that my MacBook fans kick on very shortly after watching a few clips, then eventually go on full blast. I noticed this in Leopard/newest Flip4Mac version (never had issues in Tiger). It is similar to what Flash videos do to Macs. Also, the video becomes choppy, like a very slow animated GIF.
Is there a known way to fix this? Perhaps a different Quicktime plug-in?