Looking at the pictures, it appears that, yet again, Tamron didn't bother to make the focus and zoom rings turn the correct direction. Do they not realize that the primary customer for this lens is going to be a professional who owns lenses such as the 70-200L and 17-40L?
This is a serious usability flaw, and a dealbreaker for me. A consistent user interface is critical, and Tamron has broken it here. They finally graduated to the late 20th century and added USM and IS to their lenses; would it kill them to make Canon-mount lenses that behave like Canon's own lenses?