Right, and that's a bit like trusting a site's meta keywords to fully describe the search engine keywords used to rank your site.
This is an interesting thing, because how much does a search engine exactly trust your site content, especially very specific tags like this? Not very much trust, it seems to me.
On the contrary, structured microdata is used quite often by companies like Google and Facebook to understand your site better. Here are a few examples:
Rich snippets on Google allow you to customize your snippets in search:
In fact, in the Google Webmaster Tools dashboard there is a central place where you can go to verify that the structured data Google has extracted from your site is correct (and if not, change your markup).
Facebook's Open Graph microdata format allows you to describe your site in a way that Facebook can understand. This helps when generating snippets or treating your content as media content when it gets shared on Facebook. For businesses / places they surely use this for phone numbers, address, services, etc.
Using a logo annotation, if Facebook were to make a synthetic place page for your business or company you could imagine them looking at a logo annotation on your site to decide what logo to use. This stuff is commonplace.
This is an interesting thing, because how much does a search engine exactly trust your site content, especially very specific tags like this? Not very much trust, it seems to me.