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Focus speed is fine - I have not had any focus failures either. In fact, i was shooting some close-ups on a very windy day - 15 mph, gusts to 20+ - the autofocus was on continuous and I did not get any out of focus pictures. The shutter lag was not a problem either.
I have not done any low light shooting yet.
I have not heard anything about who makes the sensor. However, I would not be surprised as Sony is a leader in CCD technology.