There is a great article by Stuart Robertson in A List Apart this week on the use of Access Keys titled, Unlocking Hidden Navigation.
What are access-keys you ask?
Access Keys (an introduced W3C standard) allows for the navigation of online content without the use of a mouse by assigning a combination of keys (eg. alt+1) to nav items.
Adding access-keys to navigation also enables people with limited mobility to access navigation by using the keyboard, voice or via a screen reader.
There are also great discussions in the article forum thread.