One dramatic improvement (I think so, at least) is that this year, most of the projectors lacking adjustable lens shift, have been redesigned compared to previous models, so that they have less fixed lens offset. Last year we had 5 projector with at least 15 inches of fixed offset. This year, that number has dropped to just one, (the Mitsubishi HC3800 at 16.5 inches offest) and only one other with at least 10 inches (that would be 12 inches for the Samsung SP-A600. The rest of the fixed lens offset projectors all have about 8 inches of offset, which is just about half of what most of last year's units offered!
The same chart we used above for throw distances has almost all the info you need for vertical positioning. It tells you if the projector has adjustable lens shift, and where the projector can be mounted, relative to screen height. Below is a list of projectors that do not have lens shift, and do have a lot of lens offset requiring them (if ceiling mounted) to be mounted higher than the top of the screen, by enough that they may not work in your room, if you don't have higher than average ceilings.
All of these units must be mounted approximately 17 inches above the top of your screen's surface. That 17 inches is the difference between the top of the screen's surface, and the center of the lens. Remember, that even mounting as close as flush to the ceiling as possible, the center of the lens is likely going to be at least 7 inches below the ceiling (and that's tight).
Below is a chart which gives several examples. It tells you how far off the floor the bottom of the screen surface (not the frame) would have to be, for four common screen sizes, and four different ceiling heights. Obviously, you can't have your screen starting just a few inches off the floor, especially if some folks sit behind others. To come up with these numbers we assume a projector without adjustable lens shift, fixed lens offset of 15 inches, and the center of the lens. We assume you can't mount the projector any higher than where the center of the lens would still be 7 inches below the ceiling (about as high as you can mount it, with a typical ceiling mount). Many mounts may require an even larger.