During the rescue scene where George steers the catamaran over the semi-conscious David, a close up of George right before he falls into the ocean shows that he is wearing prescription eye glasses. He tumbles into the water, and quickly emerges, now wearing sun glasses.
When Samantha Taylor uses the operator to phone home, she asks for a number in the 275 prefix in LA (which was all 213 area code at the time). Although George Webber home is clearly located in Malibu, the 275 prefix in the late 70s was located in Beverly Hills. Additionally, the film doesn't use the now standard convention of unassigned "555" prefix phone numbers, and gives an entire seven digit number - 275-0187.
When looking through the telescope the picture moves around as if being moved by George. But when it shows George looking through, his hands are behind his back as if he has made no attempt to move the telescope.