Ready, Set, ... iOS 6 Available at 1 PM Eastern Time, 10 AM Pacific
Fortune's Philip Elmer-DeWitt says iOS 6 will be available at 1 PM Eastern Time (US), 10 AM Pacific. The free update should be available over the air, from Settings > General > Software Update. Even if you don't rush to update, expect your device to prompt you within the next day or so.
Using MDM queries, you ought to be able to chart upgrades of your users. Are any Enterprise iOS readers willing to collect and share this data? That could be one mighty interesting chart.