I actually have a YouTube application which, AFAICT using a task killer, is launched for YouTube videos (even from the browser). Same with other webvideo and the generic "Streaming Multimedia" application I have.
My biggest gripe is that you can't background it to allow it to buffer the whole video. Seeking is also very flaky (often just tossing away all of the cache and then quitting). This is the primary reason I refuse to use flash on my main machines: mplayer just does so much better at everything than flash when it comes to video.