Pretty much. Also, MacTubes doesn't have to composite the video against the rest of the YouTube document; it can just blast it out to the screen. The QuickTime Enabler for TenFourFox is based on the same idea.
Install Niceplayer and Perian. These two help you play lots of codecs better (also flv's). I mostly use xineplayer for anything avi (divx,xvid). for you tube I use youview which is excellent. I even donated to it. My main computer is still a QS G4 867Mhz with l3 cache and 1gb ram. I rarely run anyting full screen but I can run everything correctly