I'm in a similar boat as others here, I do 500 miles/week to work and back. 5 days a week, 50 miles each way.
Coming from a 320cd BMW I'm feeling both the extra money required but also the lack of range. (My car is a bog standard DSG.) 60euro used to get me about 600miles at motorway speeds in the BMW (not holding back) but the GTI will only get me about 300miles for the same money and speeds. So, in the beginning I was getting about 30mpg sitting at motorway speeds but recently as a test I've stopped using speed and started using RPM as a marker. I sit the car at 2500rpm (about 65mph) on cruise (6th) and let the car do it's thing.
It's jumped to 450 miles in range and about 35mpg which is a huge increase. Instead of refilling on a Wednesday evening, i'm getting a full extra day and filling up on a Thursday. (the final 50 miles is in the lower quarter or less of the tank so never used).
For comparison, my TME Evo 6 used to get 280 miles from a full tank (40 litres) if you drove it like a pensioner (which you'd never do), or about 200miles if it was driven normally, (160miles if driven "properly"). I used to fill that thing 3 times a week for the same drive to work and back at 50quid a fill, it was worse than a mortgage!!
All in all the current MPG situation is not bad for a turbo engined petrol sports hatch.
HTH