We aggregate data across tons of our customers (anonymously, of course) - Mixpanel.com
I don't know but I don't believe the data. Apparently in the last couple hours people have been downgrading to iOS 5 or lower.
Could be that the active user base of mixpanel has dropped slightly while people are offline to upgrade. Would depend on exactly how their metrics are being gathered.
None-the-less I find it amazing that ~20% of their sample base is already upgraded.
This could mean more people were logging in to those particular apps from old iOs5 phones.