Has anyone used this plugin?
Yes, me... but I'm the author. Are you using the latest version? There was a small error in a previous version that didn't load the locale-specific validation functions.
I have installed both validation_reflection and client_side_validation, added class="validated" to my form, Form.Validator.installForAllValidatedForms( ); in application.js, .invalid { ... } in stylesheet. In IE 6, when I load the page I get 'object doesn't support this property ...'. In FF no error. But in both I can submit the form with erros, no javascript alert or smt...
As far as my own experience goes, client-side validation works in Firefox, IE6, and Konqueror. The fault I mentioned above may well be what's causing the problems you're seeing.
Michael