It's released by serial number, and according to Verizon it's going to be rolled out slowly. It started on May 30, and after 10 days you will be able to manually pull it if it's not pushed to you already. So June 9 will be a busy day for everyone who haven't received it by then.
Steve
I'd agree with you, but there are users that have had their Nexus from day 1, and have not received the update. I would think those would have the earliest serial numbers.