Answered my own question today re: the Garmin 640 (touchscreen, 5" diagonal LCD)... Got to see one turned on today and I was shocked at the poor readability in full sunlight at the highest brightness setting. My current 376C is easily viewable in direct sunlight on a few settings lower than full brightness. What gives? Aside from the much larger screen (larger than the 376C that I'm using), I was completely disappointed and wouldn't be able to even consider this for boating use. Also, the touchscreen didn't seem to convey any advantages over the button arrangement of the 376 and 478 series. I've been watching the evolution of all the GPS enabled smartphones and the "turn by turn" nav apps becoming native to these devices and am very disappointed that Garmin would even try to pass this unit off as anything other than appropriate for the dim lighting environment inside a car. Forget it if you've got a convertible. With LED backlit laptops becoming commonplace as well as LED flat panel TVs, you'd think an LED lit GPS would attack both the brightness issue and the battery longevity issue all at the same time. I would gladly pay a premium for a portable GPS with a much larger screen than the 376/478, LED backlit, rechargeable battery...is that too much to ask?
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