I can't imagine having to fill up every few days, a tank lasts 3 to 6 weeks on my car depending where I go as I get 700 to 800 miles per tank. The manual says it's a 10 gallon tank, but I think with the reserve it holds a little more. That's why I like fuelly, regardless whether you do 1000 miles a week, or 10 miles a week, you can get a report at the end of the year with all your averages to give a true cost of running the car.
I prefer diesels too, as even though like any other car, short urban tips use more fuel, diesels are still pretty good on fuel. I think the least my car would do around town is low 50's MPG, still perfectly acceptable in my opinion.
Ok so I've been studying my MPG over winter. There's been a big drop, so I researched when the UK starts using winter diesel, and it pretty much explains my poor economy. We start using winter diesel on 16 November. I fuelled up exactly then, and my last few tanks have been below average. We stop using winter diesel on the 16 March, coincidentally I also filled up then (my current tank) and so far my economy on this tank is significantly better, Mid 60's MPG V's late 50's MPG on the winter blend.
So for anyone wondering, you can roughly assume there's about a 5% drop using winter blended fuel. Of course everyones circumstances and journies are different, but these are my results.