Or just crawlers ignore HTML5 new-tags (like <article>, <section>, <video>, <nav>, and so on…) indexing the pages?
For example, speaking about google-crawler, I found only old articles like this (2 years ago).
Maybe the rules have been changed?!?
To be honest, I don’t think much have changed since that article was written. If you’re just thinking about using HTML5 for SEO, then don’t. However, if you want to use HTML5 for other reasons, then go ahead. A lot of HTML5 features are still not supported by all browsers so watch out for that if you care about cross-browser support when you build websites.
Personally, I’m using the HTML5 doctype when coding, but I still don’t use any of the new HTML5 elements. I do use some CSS3, but I make sure everything’s OK in all major browsers before proceeding.
Again, HTML5 won’t give you any advantage in search engine listings as far as I know, but as long as you keep your markup semantic, your content fresh and about topic you’ll climb the listings.