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.

Can you afford to make registration optional?

Couple of months ago I was buying air tickets on a travel portal, and found an interesting feature. It had a link which said, if you are in a hurry, purchase a ticket as a guest user itself. Registration was optional on that site.

I fell in love with that travel portal instantly as they gave me the customer the choice of initiating a relationship with them. I didn't have to register upfront to use their service. I bookmarked the site and made my purchase in a giffy. I did eventually register on the site on my third visit to purchase a ticket.

So what do you think, should resources such as product demos, white papers, webinars etc be hidden behind big Lead capture/Registration forms or should you just trust your customers to come back for more and initiate a dialog with you when they are ready?