I've got a Honda generator that has been sat for nearly five years since I last used it with petrol still in the tank. On the weekend we dug it out, opened the valve, waited a few seconds... and it started second pull. I had run the bowl dry when it was stored away, which probably helped... tank looked good though.
Sadly my local LPG filling station is a little bit in the wrong direction to go to all the time now, so I'm going through petrol at quite a rate :(