Wouldn't it be possible to integrate the Joomla captcha plugin into Virtuemart 2 for example in the product details ask a question page too? I receive a lot of spam emails with the ask a question. If Joomla already offers such a plugin, why does VM 2 not use it?
KeyCaptcha easily integrates with VM2 forms and IMHO is better than the J2.5 Recaptcha, which only works for Joomla registration.
http://extensions.joomla.org/extensions/access-a-security/site-security/captcha/18364