My 998 city E would give me around 44 mpg and this was a combination of town driving, A roads and country lanes. I'd do about 240 miles per tank although due to the design of the tank the petrol pump used to click off before it was actually full.
I did drive down to brighton and back once and I averaged about 40mpg while maintaining about 65mph all the time down the motorway.
To be honest compared to a lot of modern small cars they can hold their own mpg wise. This is probably due to the fact that they are much lighter than a lot of modern cars. I had a 1.2 litre Corsa as a courtesy car a week ago while my vectra was being fixed. I was only averaging about 37 mpg out of it. It really wasn't suited well to motorway and dual carriage way use. It felt worse to drive and slower than my mini did.
My mum's Suzuki swift only does about 48 mpg.