How often I use
I use HTML on a daily basis, often as razor-flavored HTML in various C#/.NET MVC applications. My workplace's website is a mix of static HTML, .NET applications with razor, and Cold Fusion pages, all of which use HTML as the base presentation layer.
My skills with HTML
I can and do write semantic, accessible HTML by properly using landmarks, ARIA attributes, and structure. I keep my styling in CSS files. I do NOT use headings simply to make text larger. In fact, I yell when I find others doing it.
I very rarely need to look up parts of the HTML specfication since I used it so frequently, but there are various elements I don't work with at all: the video element in HTML is something I don't know much about, for instance.