In an effort not to totally derail the conversation I guess I'll mention that nearly every browser is going to have some shortcut keys that would map to common emacs functions that will get swallowed by the browser.

But what I'm really wondering: what makes you say C-k (kill-line) is the most useful command ever? This is slightly inconvenient with basic Windows shortcuts (shift+end ctrl+x, approximately). I tend to think one of the functions which isn't trivially replicated in other environments is more useful. Just curious...