My gas gauge seems to be consistent, and no different that what I have in a car. It stays on full for quite some time, and then starts dipping, and after the half tank mark, dips even quicker. I have always had similar experience with cars. It seems to be consistent as far as gauge reading, miles left on tank, and miles ridden. I start thinking about gas in the 200 mile range and will ride it out to maybe 230, as long as the miles to empty still shows upper 30's to 40 miles left. At that point, I start seriously looking for a gas stop. I trust the gauges, but only so far.
My friend has an 08 SEUC and his gas gauge wouldn't reach full and showed him hovering on empty after a little over 100 miles. But it would take in the 3 gallon range to fill it back up when it showed empty. I told him that he had a problem...shop agreed...they ordered a new fuel gauge or tank floats, or whatever it is that they determined would fix the problem.
Another thing I have found is that the way the fuel opening is on my bike, when the pump shuts off, I can squeeze more gas in little spurts for quite some time to get it to actually fill up, and that's with it on the jiffy stand. If the bike was upright, I'm sure it would hold some more. That opening seems very prone to gas spitting back out at you, so you need to be patient and careful if you want to get it full. Waiting for it to stop and a few quick top offs doesn't get it full.