Rich Snippets - please help me check my understanding

I think I understand the idea of Rich Snippets. The idea is you are marking up you content to highlight which words relate to a person, business or some other thing (e.g. a movie). As of now search engines can only match keywords and Rich Snippets should help them understand that “John Smith” is a person/name and that “Skyfall” is a movie.

I believe that in doing this will allow additional content to be shown in search results (at the discretion of the search engine of course). So a movie search could show a picture of the lead actor.

Basically my questions:

(1) Does anyone care about Rich Snippets?

(2) Should I mark up every piece of content. So every person, every movie, every thing, or do I just mark up what I want a search engine to highlight in the search results description? So if the content is a movie review do I just highlight the movie rating and the film title + maybe the lead actor, or do I highlight every person name listed, and every other ‘thing’ etc. that appears on the page?

Thanks for any help.