i tested something at home.
-> it scroll back to first error or if you jump in and left it invalid
-> really easy to integrate e.g. attribute requried="requried" or maxlength="20" or type="email"
-> ajax validation like existing username is possible
colours not my fav, but its the same used in validation right now.
i used: http://flowplayer.org/tools/demos/validator/index.html
1.2.6. dev because for recheck if you disable fields with js has 1.2.5 an annoying bug.
If you test it in borwser like ff 6 use in form novalidate="novalidate", because else Browser use his html5 validation check. This js plugin works with old crappy browsers too.
Internet Explorer 6+
Translations/multilang are possible.
What you think about JS validation in ISPConfig3