My opinion: There's a definite possibility of the OS being released tomorrow, alongside anything else. However, there is a strong chance that this will not occur. In other words: We don't know when the OS will be released.
The reason why there's a good chance it could be released tomorrow is because we're already into the second half of the promised release month. So any day could be the day.
In all likelihood I'm looking at the 19th or the 26th. I'll be on vacation on the 26th, and if they release it on the 19th with the Macbook Airs I'll have to be lucky enough to get my spec'd choice (otherwise I'll have to order one and pick it up when I return from holidays).
I'll be waking up early tomorrow and on Saturday, as well as Sunday, Monday, and Tuesday all following... basically every day for a while... just to check the Apple website and head out if they do make a major release without any forewarning.
But these rumors aren't solid at all... they have no backing... they were fun at first, but it's getting annoying when these sites go ahead and cite rumors that were started by someone who wanted a little attention. It'd be nice to have more rumors that have actual proof backing them up

Ex: The rumor of Thursday (today) being the release was backed by a couple of other rumors (do not open packages, and overnighter); but the packages and the overnighter were rumors in and of themselves... so we're just stacking rumors on top of rumors and getting nowhere. Let's start with a teeny bit of fact first!

Then we can start making some inferences as to when the release should be intelligently rumored to be.