I hope it's not bad form to resurrect an aged thread? It seems appropriate in this case...
I fill up every three commutes on my Mk 3, which means between 214 and 244 miles (depending on whether I take the scenic route home). Never quite got to 18l (17.99 was the most after 242 miles).
The flashing starts before I get to work on day 3, and I have a 35-40 mile return journey before filling up in my home town.
Range is useless - I can put it in the garage with a range of 180 miles, and get it out in the morning and it's dropped to 45 overnight! Of course it attempts to count down to when the flashing starts, then disappears, so you can't use it or rely on it for anything.
Trip average mpg is pretty good - reads a couple of mpg below the real figure, but once you know that it's reliable.
I get around 60mpg (58-64 depending on weather and route), so with about 40-45 miles on the flashy, which is supposed to indicate 5.5 usable litres, I should still have another comfortable 25-30 miles left (which I don't feel like testing!).
It's a bit annoying that the flashing gauge starts about 15 miles earlier than it did on my mk1, despite the extra 2 litres of fuel in the tank. The mk1 gauge was useful, this one is crap (aside from the average mpg, which is great!), so it's back to old-skool trip meter for knowing when to fill up.