Disposable Email Addresses

I recently had a couple of users signup and download a white paper and my follow up email to the same users the very next day started bouncing from the id. The strange part was that in spite of a double opt-in registration mechanism in place, I seem to have ended up with email addresses that were valid at sign up but invalid soon after.

A little bit of googling on the domain name of the email addresses led me to
mintemail.com. They offer a nifty little service to it's users where they offer a disposable email address that's valid for 4 hours.

From a B2B marketers perspective this is a nightmare scenario as the Lead Capture campaigns could be capturing worthless contact info that expires in a few hours time.
It sure is a boon to someone who'd like to access whitepapers, surveys, case studies, podcasts...etc of a company anonymously.

Maybe it's time the email validation routine in the registration form also validates for domain names known to host disposable email addresses.