This sweet little number has got to be the best value for money going around in the 70-200mm telephoto zoom segment of the market. Being a Canon shooter, the price is about the same as the Canon 70-200mm f/4L IS.
The performance is about 90% of the Canon 70-200mm f/2.8L IS, with the Sigma a little darker in the corners, warmer picture and more noise. Build quality and quality control is improving but not as good as Canon or Nikor.
I didn't buy it because I already had a 70-200mm f/2.8L IS II, but my buddy who was looking for a 70-200mm f/4L IS bought the Sigma instead after pretty much talking himself into buying one in a about five minutes. Given the white Canon lens simply screams photo journalist, private investigator or schlub with too much money, I might get one as a 'low profile' travelling lens.
If this is a sign of the future for Sigma, things are definitely looking good.
A huge tick.
Everybody underestimates a kick to the groin - Bas Rutten