General information: I have had the GT750E projector for 4 months, and I am very happy with it. We use it daily for both 2D and 3D movies, games, TV shows, etc. It has over 430 hours of use, and the picture looks great! The setup is: 106" manual pull-down screen (on hooks - 7 3/4" - bottom edge from the ceiling) - 13' viewing distance - moderate ambient light - RF glasses (we like them).
Ceiling mount: I mounted the projector about a month after getting it. I was glad to do it since both the cables and unit were finally out of the way; and we could now use the Kinect and PS Move with it (the short-throw is ideal for this).
However, it was one of the more difficult DIY tasks I have ever done. Both the lack of zoom, and relatively large offset made the job difficult.
I have an 8' ceiling, and the AV cabinet (directly below) is 25" high from the floor. Considering the offset, his left a relatively tight space to fit a 106" image in.
First. I got the lowest profile ceiling mount I could find on the net (2.5"):
Ultra Low Profile Projector Mount LFM
Next, I got advice from other AVS Forum-ers here:
Tips for short-throw, fixed focus, 8ft ceiling projector installation?
All information in this thread is pertinent, except post #2. The the lack of zoom on this projector gave a whole new meaning to the saying: "measure twice, and cut once". By measuring very carefully, the final physical adjustments were handled by what was available on the mount - once the projector was affixed to it on the ceiling. The projector appears to be slightly pointing up.
Finally, I adjusted with the projector vertical keystone (-1), and vertical image shift (4) to fine tune the positioning. There is still a very slight keystone effect (about 1/2"), but I never notice it unless I look for it.