It would definitely help, I highly doubt spammers would use that sort of mechanism.
The solution gets around potential vendor lock-in and privacy issues with a service like Google's, but it still fundamentally shifts the problem from the service to the user (the original commentor's gripe).
I'm thinking it would probably reduce the number of users who successfully contacted you legitimately, but CAPTCHAs also do that. Do spammers actually have the email accounts they claim to and respond to confirmation emails?