Build Quality:
I own in the past Tamron SP 17-55 2.8 non VR, and the build quality was horrible. Switch to the Canon 17-55 2.8 after all the grip areas fall out of the lens. I hoped that the new looks of the Tamron SP 24-70 2.8 VR wasn't like that.
The feel of the lens its pretty impressive, and its weather sealed. Looks improved over other Tamron lenses in the past and better than the old Sigmas. Unfortunately it shares the same rubber grip and the same problems of previous Tamron lenses. All rubber in the lens falls apart over 1-2 years.
Its not meant to last forever, not even 5 years.
Recommendations:
This lens its for casual photographers, serious amateurs and travelers. Has some serious punch pack in it, great IQ, weather sealing, VR; and look cool. If you don't mind dealing with the AF Issues and missing a few shots, GO FOR IT! Its a great lens.
But if you are into the business, working in photography (weddings, journalism, or anything heavy duty), save more money and go for the Canon 24-70 F2.8 or F4 IS. Tamron SP 24-70 isn't reliable, and can't take the pressure of work over time. You will be selling it for half-price half-broken in 1 year just to go for the Canon version