Here is my proof that it doesn't effect everyone!
http://www.youtube.com/watch?v=DQBscc7jong
I filmed this 3 times, but the first two didn't have sound, in both of those previous tests holding the phone with the left hand performed equally with holding it touching it as little as possible, (Actually it performed slightly better in both cases). When I filmed this one I did have a slight drop of bars at the beginning but it had no effect on my data, and the bars recovered quickly. I believe this is more of an issue with reception in your area combined with the design of the phone, rather than a real huge issue with design of the phone. But as you can see, the left hand, and covering the black lines have no effect on the quality of the signal.
http://www.youtube.com/watch?v=DQBscc7jong
I filmed this 3 times, but the first two didn't have sound, in both of those previous tests holding the phone with the left hand performed equally with holding it touching it as little as possible, (Actually it performed slightly better in both cases). When I filmed this one I did have a slight drop of bars at the beginning but it had no effect on my data, and the bars recovered quickly. I believe this is more of an issue with reception in your area combined with the design of the phone, rather than a real huge issue with design of the phone. But as you can see, the left hand, and covering the black lines have no effect on the quality of the signal.