As I reported at Search Engine Land, Apple mobile Safari in iOS 7 and in some cases, other iOS versions, is showing more referrer data now than it did prior. Back in the day, Apple for some reason stopped showing in many cases that traffic came from Google when the search happened on Google via mobile Safari.
For example, if someone searched for blue widget using their iPhone, and clicked through to your web site from Google on mobile Safari, the data in Analytics would say it came from a "direct" source as opposed from a "search" source from Google. Why? Who knows but that is what happened and happens for many users.
With iOS 7 and some users on iOS 6, now Apple seems to be allowing the referrer data through. I am not sure who is at fault but I do think it has something to do with Google's HTTPS and how it interacts with how Apple designed mobile Safari.
A WebmasterWorld thread has webmasters complaining that the not provided keyword data has spiked to over 70%. Well, it has. But it is likely due to the fact that iOS is now reporting more search data, as opposed to it as direct. So more keywords are not passing through because it is being reported better.
Here is a chart showing the search displacement between iOS 5, iOS 6 and iOS 7 (you can use this yourself on Google Analytics by using this analytics template):
Notice how more and more organic search data is being reported as we get closer to iOS 7.
I tested this in iOS 7 myself and my referrer from Google is passing through but not via iOS 6. Some are reporting iOS 6 does pass referrer. I think it depends on the device and version of iOS 6 you are running.
Here is data showing the increase in not provided queries over time for this site:
This site now is over 70% in not provided stats, at least for the past thirty days:
Pretty wild! 70%+ of my keyword data is not provided by Google. So sad.