I'm having the same problem with my Canon 7D with LR 4.3 on MacOS 10.7 and 10.8. It worked fine with previous versions of Lightroom but it doesn't now. LR detects the camera but no images are transferred to the Mac. EOS Utility works fine.
I've been writing images to a "Camera" folder from EOS Utility and using auto import in LR as a work around but this causes delays in displaying the image in LR and confuses clients.