I recently changed the gauages and senders on my Cessna for new ones and have found them to be totally accurate. I have a FS450 fuel computer which is totally accurate and the gauges compare bang on with the fuel computer.
But it still does not stop me from dipping the tanks on every flight. I guess the fear of falling out of the sky after omitting a visual check that the gadgets are telling the truth is still as strong as it was when I first learnt!!