In a surprisingly fast move the FAQ's for 7th are here already.

I'm going to read through them now and edit this post with the important bits (as I see them) as I go.

 Nothing, this is a pathetically short FAQ. Well, next to nothing, Broodlords who cast Dominion temporarily become Synapse Creatures, which is a pretty big deal.

Shadow in the Warp was not changed, which is unsurprising but very shitty.

All of our Special Characters have lost the ability to take Catacomb Command Barges, which is shitty (especially for Anrakyr, I'll basically never take him now).

Gloom Prism now gives +2 to Deny The Witch rolls to all units within 3". The 3" range still limits its usefulness by a lot, but it's otherwise pretty solid.

Unsurprisingly all Psykers/Psychic Pilots have been given access to Daemonology. Kinda want to see a Hemlock Wraithfighter  running around summoning Daemons just for the luls.

Space Wolves:
Am I reading this wrong or did Space Wolves just lose access to all their unique psychic powers?

Chaos Space Marines:
Heldrake took a major nerf here. The flamer/autocannon is now Hull Mounted (45 degree arc of fire out front) instead of Turret Mounted (any direction). No more flying over a unit and then froshing it.

Tau Empire:
Disruption Pods grant +1 Cover Save to their model now. Unless I'm mistaken it used to be Stealth right? Or is this an old change?

Nope, Orks lost all their powers to.

Sisters of Battle:
No FAQ for you. GW doesn't think you're a real army anyways.

So instead of updating the Powers with a couple lines of text to bring them in line with the new edition (something that would take 5 minutes) GW would rather just can every pre-6th Edition Codex powers. That is... that's actually really offensive to me. That's just a huge FU to the players of those armies.