I received the Plexiglass rear projection screen from Evonik Röhm today! It was packaged in a big blue plastic cover to allow it to withstand collisions. This turned out to be a good thing because there was quite a dent in the packaging, but fortunately not even a scratch on the Plexiglass.
The Plexiglass sheet was cut to my exact measurements (776mm x 588mm x 5mm) and fit beautifully when I did a test fitting.
As you can see from the picture it was also covered in a protective lining. Its a nice darkish grey and really feels good to the touch. In case you're wondering what that bright spot on the right side is... those would be my grubby fingers. ;-)
Since I'd heard some people mention that this stuff easily scratches when scratched with hard objects, I thought I might as well provide it with a nice seating in my table top. 
So, I've been adding leather strips to the bottom of the rim in my table top that will hold the screen. The idea is that it will protect the screen from the wooden rim it's resting on.
See the picture on the left to get an idea of what I'm doing.
A nice side effect of this leather lining is that it provides for a sort of cushion which causes it to make less noise when I put in the screen. It also provides a dark edge on my screen making it look even nicer.