The official release for SB has been reported to be the 9th. Leaks of Microcenters SB sale prices suggest the embargo lifts at this time. I've seen forum posts from people who tried to sweet talk the Microcenter guy to pull CPUs 'from the back'. It sounded like they'd sell motherboards, but not the CPUs. So... it sounds like stuff is in stock.. just wrapped up tight until Sunday.
Stores don't want to risk getting sued... and/or having their CPU supply jeopardized just by selling an few CPUs early...
So... I'd expect B&M and e-tailers to sell them as soon as they can this Sunday... I wouldn't be surprised if Newegg and friends go live 12:01am PST... (so at least the lower 48 are in 'Sunday') like the release of a Harry Potter movie or something... It could be later... but they're itching to sell them as much as we're itching to buy 'em