I've tested the new 7.1 FS for some time now, and have (as is my habit) picked up reports from other users... most of whom are techs. My experiences (and verifications):
* #1 complaint: Crashing during teleports. I'm on a gamer system with a good GPU, yet have been crashing on TPS at least once or twice a day. I never used to crash on the prior viewer. Ever.
* While there are claims that PBR is leaner and faster than the old system, FPS reports are significantly lower than the prior viewer.
* Rezzing is slow. This may tie in with the lowered FPS; there seems to be bottlenecks somewhere.
* Dark and super-bright. Graphics in general are much darker, and glows much brighter. This makes vendors hard to see if they're not on fullbright, and items with glow are almost blinding. For the first time ever... I have had to start using facelights on my avatars just so their faces don't look like they're hidden under a dark hood. My skins look much darker than they did prior... especially if I use shadows. As a result, I leave shadows turned off.
* Shadows are unnatural and darken the entire scene. To get any semblance of acceptable brightness I have to turn shadows completely off. I recognize I can enhance the brightness of the scene in general (once this was called "gamma")... but that just makes the glow items even brighter and washes out lighter items almost entirely.
* There's no way (that I can find) to turn off "reflections" entirely... and these DO slow down the system. We can turn off mirrors and even set reflections to manual... but I get the feeling that even the existence of the reflection engine slows the system.
*When I leave mirrors OFF my movement is smooth as would be expected. When I turn mirrors ON my movement turns to glitchy "robotic" frames of movement, especially if I'm in front of a mirror-- as if the system is presenting a quick "slideshow" of my reflection rather than a smooth experience. And frankly, neither I nor anyone I've spoken to gives a hoot about mirrors. "Interesting special effect but no real value" is the most positive description I've heard thus far.
* Regular textures and gamma of textures simply do not look the same, even if one WANTS them to look the same as they did. PBR is changing the appearance even of non-PBR items... something perhaps it really shouldn't do.
This is just the tip of the iceberg of comments I've heard about PBR and my own experiences. For some people (merchants, creators) perhaps PBR is wonderful. For the average user... maybe not so much.