Just chiming in, as I frequent a forum that often contains illicit links...
The Core books were out weeks early (as I'm sure ENWorlders remember, people started answering detailed questions about the rules weeks before the actual launch) and those were printer leaks. Somebody at the printer got the copies and posted them online.
Every book since then has been out the day it was released - usually a legally bought PDF that had the visible watermarks removed from them. That's what happened with PHB2. The first copies I saw posted still had watermarks on them by somebody who "didn't care" and then followed up about an hour later by somebody who did remove the visible watermarks. These were posted at around 3:30am Eastern, after the official PDFs were posted at 3am for download from the legit sites.
Without an official PDF it's going to take somebody buying the book, removing the binding, scanning it, (likely) OCRing it, and posting it. It's now 9:30pm Eastern and I would be surprised if it wasn't out by tomorrow at this time. Heck, it could be out somewhere now, but I'm still at work and can't check the site. But I expect tomorrow night at the latest. The pirates will always get what they want.
Please note: I have bought every 4e source book except the adventures and Forgotten Realms source books, since my game is a homebrew world.