I just got a cheap laser pointer to use as an aid in aligning my projector to my (wall) screen. However while rolling it around on a table while projecting on to a wall, I noticed that the dot moves up and down, so the beam is not aligned with the housing. I guess there's no particular reason it should be.
All is not lost, however, I can just mark which orientation of the case gives the furthest vertical deflection (so the error is all up or down) and use that to align things horizontally.
(I got the $7.99 keychain version by Clearline Concepts at Office Depot here in the midwestern U.S. I like that the case is totally cylindrical, with no obtruding pocket clip.
I had an idea to drill a hole for the pointer in a chunk of wood, using a drill press, so I can sight back from the wall to the projector. When that beam is centered horizontally on the projector and the beam from the projector centered on the screen I'll have things lined up.)