One detail that I haven't seen in the news is that Google have been signing rights holders for quite some time now. Mike Cane tipped me to this PDF a couple weeks ago. (It's a welcome letter for GE.) I was little surprised because most every article I'd read on GE discussed the future launch and the PDF assumes GE is currently running.
I followed the suggestion of the welcome letter and I created a Google Books Partner account. Sure enough, there was a tab for Google Editions. I've read it a couple times now, and it appears to have all the parts of a contract that you'd expect between an author and publisher (or distributor, ebookstore, etc). And that tab has been there for at least 3 or 4 weeks now.
There's actually more than just the tab. The FAQ for GE is already available. I can't tell when it was posted, but it seems pretty complete to me.
I don't know when GE will be opened, but I do know that Google have certainly laid the groundwork.