Though it’s on the edge of programming questions, I think this is still relevant here, as only those of us actually doing the coding for a site would be considering this.
I’ve been reading more about keyword placement, and it seems to me like a good place to do keyword placement would be in the class and id names chosen for the elements they are representing. I’m not talking about any kind of black-hat keyword stuffing thing but real legitimate use of descriptive keywords for elements.
Is this something that is actively done for SEO?
Nope.
Search engines might look for microdata / microformats / rich snippets, but that doesn’t mean they are actively scanning every classname and/or ID.