Ajax powered feedback form

I completely understand these points, and taken no offence; I'll answer in order:

Added functionnality is enhanced/snappier user experience while being unobtrusive and requiring minimal to none modifications to the existing structure, and above all, no inline javascript or whatsoever, thus achieving enhanced functionnality without sacrificing coding style nor "degraded" (read standard) user experience.

Main benefit is: No reloading of pages, and on some user-heavy sites, drupal can be slow to output a page : when you get the form right from the first time, this is a minimal gain, but if you make mistakes submitting the form, and have to fill it again, and eventually twice, this can be frustrating.
Forms and server-side validation IMHO are the one component on the web that frustrate users and can benefit from asynchronous updates, because they have to eventually fill some info and then correct, and even sometimes, re-type some info that's already been typed.

Secondary benefit would be: This could also be the foundation to a realtime server-side validation of the forms (more secure and flexible than client-side only javascript, because it still would work on javascript-disabled browsers, with one set of rules and one implementation).

The licenses:
Prototype.js :

Copyright (c) 2005 Sam Stephenson

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

Behaviour.js:
BSD Licensed

Script.aculo.us:
"MIT-style license"

    Copyright (c) 2005 Thomas Fuchs (http://script.aculo.us, http://mir.aculo.us)
      
      Permission is hereby granted, free of charge, to any person obtaining
      a copy of this software and associated documentation files (the
      "Software"), to deal in the Software without restriction, including
      without limitation the rights to use, copy, modify, merge, publish,
      distribute, sublicense, and/or sell copies of the Software, and to
      permit persons to whom the Software is furnished to do so, subject to
      the following conditions:
      
      The above copyright notice and this permission notice shall be
      included in all copies or substantial portions of the Software.
      
      THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
      EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
      MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
      NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
      LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
      OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
      WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

On a broader spectrum, I think that these libraries would be the magic bullet to almost all drupal js needs, instead of building drupal specific js, and having them duplicate the functionnality of these libraries, (I already have to use both on my test installation).
But this is out of the scope of this discussion

Lastly, I'll try and take the time to make a patch.