In Safari in 10.5, I created a "web clip" for the YouTube "videos being watched right now" area -- just press the Web Clip toolbar button, move the highlight area over this section of the screen, and press Add.

What's really neat about this particular web clip is that if I you click on a video in the Dashboard widget, it plays directly in the web clip itself! Basically, you can view a YouTube video without leaving the Dashboard. Normally, these links open in a regular Safari window (or your default browser). I created a short YouTube demonstration of this feature in action.