Other than whacking your head, I can't think of any problems. Depending on the screen you go with, you WANT some angle between the projector and the screen but you don't need a great deal. It's actually better to have the project lens center pretty close to the top of the screen so you don't have to use so much lens shift.
I've been playing with my Stewart Firehawk the last day or so. So far I'm more than impressed. It's a lot darker grey than my last screen, but the image is brighter. I had to recalibrate my projector brightness and contrast a fair amount (reduce both). Even with the blinds open on the window I get a great picture.
If you know how to take a good screen shot with a dig camera and give me some tips, I'll take some screen shots and post them.
