I'd just like to reference http://drupal.org/project/placeholder since placeholder values seem like a really nice usability feature with HTML5.
Presently there is just a Drupal 6 version of this code, but it's essentially just a function & some javascript so really think it might be better placed in a larger set of HTML5 tools.
I haven't seen any discussion about this, so this might be a really short thread, but I'm hoping to incorporate this in a Drupal 7 - HTML5 site.