Say "interface design" and most people think of computers and how we interact with them. Truth be told, interface design is all around us. It really has little to do with computers.
My prime example of interface design is a restaurant menu.

Subtlety is more than attention to detail. Attention to detail is looking beyond the spell-check engine's declaration that 'where' and 'wear' or 'their' and 'there' are all spelled correctly, in spite of the fact only two of them are correct for any given situation. Subtlety is font choice, leading, page size and image tone. In the case of a presentation, subtlety includes slide builds, transitions, text sizing and line length.