I for one could really benefit from a seminar or "cheat sheet" on how to expand functionality on our hosted websites.
Topics such as HTML, CSS, etc.
Has OR given any thought to having such a presentation?
Not really, as that's kind of out of scope for OwnerRez. We can certainly point you to where you'd want to use HTML and CSS in our Hosted Websites, but as for HTML and CSS themselves, there are a great many resources on the Internet to learn about them better than we could reasonably teach.
We do have some snippets of useful CSS available in the support docs: