Here's a double-set of experimental bookmarklets I made the other day after getting rather envious of IE5Mac's autofill-form ability. To use, drag the links to your Links-bar:

!GET - loops thru all form fields on a page and stores values in a cookie named 'formfields'.

!PUT - fills all form fields in current page based on value of cookie 'formfields'.

(Note: use at own risk.)

Update 020115: One problem with these is that they also get and set hidden input values - messing up some web-apps... So be careful, please ;)