I was seriously considering buying this lens, debating between it and the Canon 24-70 2.8 II. But, this review along with experience of others with bad copes has made rule out buying the Tamron.
The copy Photozone (http://www.photozone.de/canon_eos_ff/741-tamron2470f28eosff
) tested was very good and Dustin Abbot http://www.canonrumors.com/forum/index.php?topic=11251.0
has a very good copy.
However, TDP had to go through 3 lenses before getting a good one. A friend of mine who is a professional wedding photographer purchased one from B&H. He has received and returned 4 lenses and still has not received a decent copy. All had AF issues and the others were sharp on one side and soft on the other. Once lens front focused badly and was not correctable at AFMA +20. Sounds like Tamron has some serious QA issues...
Personally, I don't want to go through the hassle of trying to find a good copy. I could get lucky, but evidence says the odds are against it.