Anyway to 'save' text from form textboxes before submission?

[john]

With dodgy internet connections and even dodgier hosts the forms on my site
sometimes don't get submitted properly and I get irate users saying they
spent ages writing the content into the textbox, only to have it disappear
if it doesn't submit properly. Is there anyway of making sure the text is
still there if they hit the back button if the form doesn't work? I've seen
this happen myself on some forms, but it doesn't on mine - is it because
they're on PHP pages and perhaps automatically refreshed on going back to
them?

Or I wondered if there was javascripot for saving the text somehow on the
submit button mousedown, and loading it back in the text box if the form
fails and the user goes back to it - any one got any suggestions?

Thanks

John