Synthetic Oil?

[MAC]

I have never use synthetic oil before, and I never had any problem with any engine in any car in 20+ years of driving. Sure, lots of things go wrong and needed repair, but never the engine, which made me think the engine is the strongest part of a car. I see these late night infomercial on TV, selling gas addictives and promising all sort of miracles, then I read in car magazines telling me these are useless and stay away from them. There are people who will put Premium gas in vehicles recommended regular gas, and I have seen reports and interviews saying it is a total waste to do that. TV reporters also have reported that expensive big brands gas came from exact same wholesale refinery as the cheap gas, research showed they are exactly the same gas from the tubes, yet I know people pay lots more for bigger branded gas.

Naturally I am confused and I want my Hummer to live a long and happy life.
If synthetic oil is so good, why auto maker do not recommend it? Can you please tell me what are the proven benefits of synthetic oil that you yourself have experienced. Not just better or good for engine, but something solid, real and can be noticed. Faster? more MPG? more HP? Quieter?