I've used the old Tamron 28-300mm (1.5x crop = 42-450mm) on a Nikon D100 for a few years.
It obviously wasn't the best lens but worked well for our purposes shooting party girl content in a variety of situations. I definitely couldn't have been changing lenses in the middle of Mardi Gras or on the beach in Cancun.
On your Canon (1.6x crop factor) that lens would be a ~28mm to 432mm. That's a great coverage range.
There are a bunch of user reviews on Amazon and a pro review at DPReview.com.
http://www.amazon.com/Tamron-18-270m.../dp/B001DYC0CS
http://www.dpreview.com/lensreviews/...p5-6p3_vc_n15/
I'd say go for it.