Thanks for the response. I quite agree and having thought about it I realise it is more than just a gimmick/demo.

As an example, I was thinking in terms of a captcha ad-on I know of for a CMS that – to prevent core code hacking – adds an intermediate page with the captach image on it, this is quite frustrating. Now, with an Ajax solution like yours this can, as you say, provide the user with a more pleasing result. And the backend check can be left in (with dummy pages, etc. if needed) to stop the nasty bots from spamming.

Now, back to writing the Ajax solution… ;)

Never use it client-side validation as a replacement for serverside validation. That’s a completely different story. Of course the goal is to write validation rules once and run them on both sides, once for helping the user, once to keep gargabe out.

One I just don’t quite get though is the Ajax ‘captcha’ (http://jquery.bassistance.de/validate/demo/captcha/index.php). At first I though Wow, that’s great I can build captach in to any page easily. But then I realised that the process must be repeated on form/page submit anyway in cases where JavaScript is turned off. So perhaps it’s not as useful as I first though for real spam protection – or have I missed something?