haha...I just set my clock to June 20th, rebooted and got the pink screen. Then I ran a restore using Organizer and when it was done it still said it was expired.
Good thing this isn't my only unit. No laggy beta for me for a few weeks.
EDIT: Tried doing it in iTunes and it worked.
I messed around with the date and it definitely expires on June 19th. I'd speculate that the next beta will include features that haven't yet been announced so it won't be released until sometime after the keynote on the 8th.