had been using this lens for the past few weeks. a great combination with my 70-200 f2.8 IS.
only used this 2 lens to cover an indoor event with low lightings. 95% of photo are sharp. rest of 5% is either due to slow refresh rate of my flash, the stupid coloured spot lights or my hand shake.
Focusing speed is almost as fast as my canon 70-200 f2.8 IS but a little noisier (cant hear when in the noisty event I covered.
For the price (i bought 2nd hand) it a steal vs the original canon version.
Someone mentioned that its soft wide open but i have not tested it yet. will do so when free.