When prompted for a Captcha by SU, There's no visible captcha text and no input box. The only thing visible is the "I'm a human" button.

Windows XP, FireFox 4

Form Source:

        <form method="post" action="/captcha?s=47e22f3a-3f5c-4c8c-8df9-c9b24b7b19e5">                
            <div><script type="text/javascript">
        var RecaptchaOptions = {
            theme : 'clean',
            tabindex : 0
        };

</script><script type="text/javascript" src="http://api.recaptcha.net/challenge?k=6LcDNwYAAAAAAG_X1rC8kTtLBP6XS2Ym1N0n9kSY">

</script><noscript>
        <iframe src="http://api.recaptcha.net/noscript?k=6LcDNwYAAAAAAG_X1rC8kTtLBP6XS2Ym1N0n9kSY" width="500" height="300" frameborder="0">

        </iframe><br>

        </br><textarea name="recaptcha_challenge_field" rows="3" cols="40"></textarea><input name="recaptcha_response_field" value="manual_challenge" type="hidden" />
</noscript></div>
            <script type="text/javascript">
                $(function() { $("#recaptcha_response_field").focus(); });
            </script>
            <noscript>
                You must enter the confirmation code in the box above after solving the challenge
            </noscript>

            <p>
            </p>
            <input id="btn-captcha" style="font-weight: bold;" type="submit" name="post" value="&nbsp;I'm a Human Being&nbsp;" /><br>
        </form>