Please don't suddenly and randomly flip the value of the "Always use the cursor keys to navigate within pages" option. Having the down-arrow key change from "scroll the window down a few pixels" to "jump to the next link" is brain-shearingly annoying.
Dear Web Application Programmers,
If your web page presents a very complex form to fill out, which can take up to 20 minutes to do correctly, PLEASE program it so that if the user hits Backspace when not actually clicked into a form entry field, it doesn't just happily do the equivalent of hitting the Back button. I.e. ask me if I really want to navigate away from the form I just spent 20 minutes filling in and let me click "no" so I don't scream "NO!" and want to poke out my own eye.
A Nearly One-Eyed Ranting Nerd