I remember a thread on this a while back, and since i just had my emptiest tank ever i thought i'd fill you guys in!
Been driving with the light on for a couple of days (short commute) watching the computer count down from 60 odd. Today on the way to find a decent petrol station it went from 25 to 18, then just started flashing -- --, wasn't convinced i was going to make it!
still, managed probably 2 miles after that point and managed to squeeze in 71.21 litres
Sorry Z, i wont let you get in that state again