Has anyone implemented a combination of coaching and captcha?
For example, Joe User wants to upload a file, is presented with a coaching page that incorporates both an input box to input joe.user (which could potentially be checked against a MWG list) and a captcha with an input box for the captcha data to be submitted.
If joe.user is in MWG list AND captcha data is successful, Joe User's request is processed. If not, the request fails.
Very interesting. I am pretty sure that you can configure MWG to speak with a captcha backend. Googles Recaptcha (http://www.google.com/recaptcha) has a Web API that you can query, so it should be possible to use external lists to communicate with the backend for validation of the input.
Unfortunately I have not set it up and don't have any free time to play around with it. However if you want to give it a try I am interested to see the results :-)