A bit later, Chris Messina suggested a slider control. Not much later, it was finished. It degrades to a plain select box, which is where the slider values are taken from. Its main purpose is to be used to select between options, and not for arbitrary continuous ranges.
These will soon be coming to a Drupal site near you after some more polishing and bug testing. Whether they will be used in Drupal 4.7 remains to be seen (though I can already think of a few spots where they would be useful).
Yay for open-source developer cross pollination :).