Modern web browsers are capable of automatically filling in forms with common information (for instance, your name). However, there's no standard way of indicating what a form's for, so deciding what field should contain what is largely guesswork.
I'd like it if a form could declare "I'm a weblog comments form", so Mozilla could fill in my name and mail address (after asking me for confirmation — we don't want this to be a privacy risk). You could do this by declaring the form to have a well-known class; once you've filled in a form with that class once, your browser remembers how you filled it in for the future.