ENWorld has a Pathfinder 2 megathread #tabletop #rpg http://www.enworld.org/forum/showthread.php?622877-Pathfinder-2nd-Edition-Compiled-Info of all the info known so far, collected in one place.
Fumbles, with mechanical bad effects, are officially part of the core rules. For any d20 roll, not just attacks or saves. And when you roll 10 under the DC, not just nat 1s.
@HufflepuffBR I don't know about similarities to GURPS, I've only had a bad experience with the system (but willing to try again).
The only info I have is at the listed thread. The full playtest document itself doesn't release until August.