Rated 5 out of 5 stars
Just started playing with this, but for those that wander how this works, go to any textarea and use CTRL-N and CTRL-P to go to previous or next line.
This already works on linux, but not on Mac or Windows.
On all platforms, however, emacs style shortcuts work in rich text editors like http://developer.yahoo.com/yui/examples/editor/flickr_editor.html
only with this extension.
The config window shows how you can customize the keystrokes, but I'm happy with the defaults. :-)