Hi,
It is interesting to me that he commented that the focusing is slow. I have the Canon 40D with a couple of Canon L lenses. I took a Tamron photo seminar a couple of weeks ago and had the chance to use their SP AF 200-500 f5.6-6.3 Di lens. We were outdoors, mid-morning. I was using a tripod. Every shot I took was blurred..EVERY single one! Really no keepers for the whole day. So, even though I learned alot at the seminar, I was pretty disappointed with my images.
This is my only experience with Tamron, and I realize that I might have been using a bad copy of the lens, but given all of that, my advice would be to tread carefully. I would ask the salesman at the shop if you can try the lens on your camera to make sure the results are within your expectations before you spend the money on it. Even though it is less expensive than a comparable Canon lens, it is still alot of money to spend if you are ultimately not happy with the results it produces.