I picked up the 50" on Friday and I would say it has DSE. I only notice it on white/grey backgrounds though when the camera is panning left-right. As such, you can see it in hockey the most, otherwise it's not typically noticeable. I'm kind of used to this effect though since my monitor (Dell U2711) suffers from a similar fate due to it's coating.
It's definitely a lot more glossy then I had expected. No visible backlight bleed though and no cloudiness. I do notice that HD content seems to be a must, SD content looks worse than my previous KDL-46V5100. Also it seems the built-in apps have surprisingly good PQ too, the demo clips from the Sony app look superb and even playing YouTube looks great too.
I can't seem to get Miracast/screen mirroring to work fully with my Nexus 4. I have to disable HDCP on the phone just to get anything to display, but it's extremely laggy and basically unusable. It didn't work at all out of the box though, only worked after the software updates, so maybe future updates will improve upon this.
ARC works perfectly with my Denon AVR-1612 along with CEC.
Mine seems to sit straight and level, though it took a bit of wiggling to get it to fully sit into the stand properly. Before that, it was tilted back quite a bit.
Still tinkering with settings though, probably will have to get a calibration disk to assist.