Of 46 total sponsors, only 6 have IPv6 enabled on their website, or approximately 13%. It should also be noted that this does not indicate whether these companies have IPv6 support in their product, only that they've cleared the simple hurdle of enabling it for their website.
Particularly interesting here is the one site that is hosted on Amazon. Their site is hosted on a legacy load balancer, which new accounts (VPC) cannot use. I am somewhat hopeful that more Amazon hosted sites will begin to leverage the recently announced IPv6 on CloudFront in the near future.
I plan to continue to meet with folk at these sorts of events and explain the benefits of IPv6 for their projects and the future of the Internet. Hopefully next year's numbers will be much improved.