Is anyone downloading the developer preview for WP 8.1?

Dear Tribe,

It's clear what my post is about, but I am also wondering about a couple of things about downloading the preview on my Lumia 1520, hope I'd get a reply from people of expertise at this matter.

  1. If this update caused any problems / had some unforgivable bugs, will there be a way to revert it to how it was (will doing a hard reset restore your phone to the firmware and OS version it had before the update?)

  2. Since I know that some of Lumia's updates are even related to the core of the OS, so will this update affect any Nokia changes to the OS? Things like the Nokia camera SDK that is found in the Lumia 1520 for instance and how it makes use of the 20 MP sensor. Another example is Nokia's storage managing apps that required manipulating some deep leveled stuff at the OS. Yet another example is double tap to wake up, and screen sensitivity which also required lots of work changing the OS to adapt to new hardware. Will any of those be affected by this update since it's not Lumia-specific and probably doesn't contain all the changes that Nokia made to the OS itself?
Waiting for your comments. Cheers! :)