That price is for an imported grey market lens that does not have any kind of warranty from tamaron which may or may not be important but needs to be stated. If you get the USA version the price is pretty much the same. I based my opinion on reviews that I have read on the tamaron, I didn't say the tamaron wasn't a good lens but at an equal price I prefer canon lenses, I have sat through a couple of classes that compared the internals manufacturing of canon lenses vs the compitition granted the class was put on by a canon sales rep but they were pretty convincing. Still doesn't mean I won't buy anything that isn't canon I own a couple tamaron lenses in addition to my canon lenses most of the issues they addressed probably won't be an issue for the consumer anyway.
As far as better IQ, I have heard that but the comparison pictures were very difficult to see the differences also probably not much of an issue on a crop body, I also prefer the internal focusing and for aquarium pics I prefer having the closer minimum focusing distance. My recomendation was not entirely based on it being a canon there were some features that I prefer over the tamaron. Both lenses are very sharp and I did just run across a $90 mail in rebate for the Tamaron USA model if you purchase before 7/31/08. Are the features on the canon worth an extra $100? Depends on the user.