I just went over to their website to check things out. The deal is good if you are buying their most expensive cards, which I didn't even bother finding. If you're just buying their normal cards, it actually only saves a few dollars. It's worth it to me to hold out a bit to see if Shut ter fly does their same free-cards-for-blogging thing they did last year.
Re: Has anyone used Mixbook?
I'm hoping for this again too!
The Blog