This is kind of OT for this post, but no, nothing to do with CSS, and yes, I have rich snippets on every site (my own and for clients) that I've implemented them. Events on my sites, and products on my clients. It's really not that difficult when you put your mind to it.
I can't say it improves ranking (as far as I know) but it does seem to help with click through, and at the very least, I really like how it looks.
My event stuff shows up great; I've just adding a rating / review capability and hope that will eventually show up too. You don't have to be a big site to have snippets shown, and you don't even have to be in the first couple results. You just have to implement it correctly.