I really like what Sigma has been doing. First, the docking station for lens firmware changes and now the mount replacement service.
And, I like that Sigma, Tamron and Tokina are all putting out higher quality lenses. We can only benefit from the competition.
I'm sure Canon and Nikon are worried about this trend. I just hope they respond by producing better and more affordable products, instead of just trying to cripple the third party products.