Here’s an article from Cisco about DKIM uptake.
Point of the article is to say that yes, more and more people are adopting DKIM, so that’s good for the cause (visit Online Trust Alliance).
Juicy deliverability morsel from the article: "Google and Yahoo! have announced that messages with valid DKIM signatures, where the domain has established a good reputation with them, are less likely to be classified as spam." And a quick reminder to our own customers that yes, DKIM authentication is baked into MailChimp.