I’ve given a couple of wedesign workshops, and one thing that makes it easy to explain is the div element. It just works as a box, and you have them nested. And that’s it.
Now with HTML5, there are a lot of new tags that somehow have the same function as div, but for special kinds of content. Article, aside, nav, etc…
While they help to organize the content in a semantic way (instead of using classes like in microformats), it raises the entry level on HTML a little bit. On the other hand it speeds javascript execution by using getElementByTagName, which might be really useful in full blown web applications.