It's improtant for anyone still reading this thread to remember that each bike is different and our reserves will be slightly different as well due to the float arm. If you've pulled the fuel pump from the FJR's tank, you will note that it's a tight fit to get it in and out and that the float arm is easy to tweak in the process.
It's good to know how much reserve you have for your riding style, your area's gas, (CA squirrel piss gives less range), and your bike. I don't get nervous until 50 on reserve, but for the reasons Radman stated, I generally get gas as soon as the bar starts flashing, if not sooner. Depends on the ride and the convenience of the stations. If I know where they are, I might head for one I like instead of just hitting the next one.
Oh, and Howie, fuel/air
ratio. If the ratio is wrong, no boom. And there's actually a pretty narrow ratio where gas ignights. Now, when you convert your FJR to alcohol, then we all want to watch.......from a distance! when you fill your tank.