I've averaged almost 39mpg on a mix of A & B roads & motorway. Did 220 miles from south Wales to Wellington (Somerset) and back on just over 1/4 tank!
Filled it right up though, needle didn't move from full until I'd done almost 50 miles...
Day to day average (work & back) I normally see 26-28mpg, although I have to go with the flow of traffic, not many overtaking opportunities
On the "real time" mpg thing, I'm almost certain I've seen it go to negative figures though! lol