Speckle phenomena are common when scanning fat patients. Many scanners offer ways to somehow overcome this effect in a limited approach. Of course, digital imaging is a lot better. I have not heard about it. It depends of the factors included in the survey.
Sonography is a highly operator dependable procedure and results can vary much.
No system is perfect. In my personal experience, I have found ultrasonography being more accurate than CT and X-rays when dealing with abdominal and muscle pathology. Also found breast sonograms being a lot better than X-ray mammography and diagnostic laparoscopy. I have also seen absolutely wrong and useless sonograms. It is very relative.