What kinds of commercial uses of the YouTube website are prohibited and which aren't?

We've updated our Terms of Use to clarify what kinds of uses of the website and the YouTube Embeddable Player are permitted. We don't want to discourage you from putting the occasional YouTube video in your blog to comment on it or show your readers a video that you like, even if you have general-purpose ads somewhere on your blog. We will, however, enforce our Terms of Use against, say, a website that does nothing more than aggregate a bunch of embedded YouTube videos and intentionally tries to generate ad revenue from them.