They used to work, now they don't so much. A couple of years ago the load article keyboard shortcut went missing. This means I can look up and down the page of articles (j/k etc.), but never load the article, or RTFA without moving to a mouse (or using a browser plugin that allows me to do this).
Pressing Tab should visually highlight the current element (it doesn't)
Broken keyboard interation changed my interaction with the site from daily use (almost every single day since launch) to once every few days.