I can't comment on the Tamron, so I guess this is somewhat pitiful, but I accept that. However, I feel strongly on this one.
I own the 24-70 2.8 II and a number of other L lenses. Honestly, some of the L lenses I like a lot, some I love. This lens is far and away the best one I own and it was worth the money. I wouldn't consider a third party substitute. So my disclaimer- I am biased, but this is a great lens. Is it worth the money, yes.
In reading the article, I must say that my "opinion" however is as irrelevant and unfair as is Austin's is, as I have not used the Tamron lens.
For those interested in my thoughts if the Canon is worth the price premium over the Tamron, take a look here:
If you don't care, please disregard... If you disagree, state your objections below.