Paul Weaver wrote:
In a decent browser you should be able to hit "back" and go back to
the previous page where your form will still be filled in...

Certainly can with Firefox, however with google the form will be hidden
- you'll have to click the "reply" button on the post you replied to.

Last time I used internet explorer click "back" lost everything you
typed, but as IE is so far behind on useful and essential features,
doesn't run on my personal computers, and is a security hole, I can't
be bothered checking.

When using Google Groups I always use the reply option that only
appears when you click on the 'show options' link. This brings up a new
composition screen that crucially includes quoted text from the post
you are replying to. Plus (when using Firefox at least) if you do
something stupid you can click the back button and what you've written
will still be there.