I put a UV Project Modifier on a Suzanne. I added an image plane with the texture I want to project onto Suzanne and positioned it.
Note: The texture is not showing as transparent in the screen shot because I forgot to check the settings for that in the menu when I used the Add Images as Planes add-on, but trust me that the texture does have alpha data.
I UV unwrapped Suzanne. The Image plane is already UV unwrapped because the add-on takes care of that. In the modifier's settings I specified the image plane as the projector object. I specified the UV map to be the only one that exists on my Suzanne ("UV Map"). I did not specify an image because I understand this is for Blender Internal only (correct me if I am mistaken - also I tried this once just in case but it made no difference).
I created a Cycles material for Suzanne that uses the image from the image plane, and specified the coordinates to be from Suzanne's the UV map (which I expected to be modified by the modifier). The alpha from the image is supposed to factor between a plain Diffuse Shader and a textured one. However, nothing is showing up at all and although I read the Blender manual page on the UV Project Modifier I did not glean any answers from it. Can somebody please tell me what I've missed?