make sure that the switch on the lens is set to MF not AF.. this should release the motor drive part that makes it stiff!

Try this link. It should help.

I haven't used the AF yet it's been on MF all the time. I'm going to return it today to B&H and try a different one.

I've been struggling with the same issues as I choose lenses for my 7D. My goal is to find lenses I can keep for the next few bodies as these cameras evolve (also I'm sometimes required to rent a 5D). One of the things that made me reluctantly stay away from the 17-55, aside from the EF-S format, is that it's just not as silky smooth to focus and zoom with as the L zooms. I went with the 16-35L and have not been disappointed in that regard. I do miss the extra 20mm of focal length. IS would be interesting to try, though I've been operating small hand held cine cameras for so long without electronic assistance that I rarely have any issues regarding unwanted camera movement.