Or at least, use it until you see a noticable difference in engine performance. If I notice my engines are no longer running up to snuff, and I suspect it's the fuel, I may keep the fuel aroung for burning in some old two strokes that are in planes that don't require top performance.

Once it gets really bad, I give it to my wife to use as perfume and/or air freshener (I can't get enough of that smell!).