Have I seen it? Yes.
Do I trust it? Yes, though I wonder how old it is.
What do I think of it? I'm a big fan, not because it gives grey knights a boost, but because it gives Grey Knights many many options. It reminds me alot of the Chaos codex in that it allows you to pick what type for army you want. Ironically despite becoming Codex Grey Knights, this list actually also opens up the Inquisition side too and i could quite viably see both DeathWatch and Sisters of Battle squads finding a home under the one book.
What does it mean for me? An eager wait for the next 2 months to see what's actually in the book and possibly a serious requisitioning of models from both my unpainted Dark Angels and fledgling GeneStealer Cult.
Progress Report: 4 Highelves done, 6 more Sword Masters to go before the first unit is done