How much markup is too much markup in an RSS feed?

The feeds I like the best are ones that use "normal" HTML, embedding hyperlinks, displaying images and applying slight inline formatting of the data I crave so badly. I get what I'm after - the basic text, and I don't always have to visit the core site to get at it.

But where do we draw the line when such formatting becomes too much such formatting? Since the content within feeds is usually basic HTML, will people start to embed JavaScript routines to create interactive feeds? Or reference Flash animations? At what point will distributing data via RSS syndication get too overboard?