An old thread but thought I'd offer my experience of the 3.0TDi quattro. Had my 07 for 34 months and purchased with sub 80k and for £8.5k in saloon guise
I've had mine remapped for economy and have never had less than 700 miles from a tank and am doing 11k per annum. Best case I've had 920 miles from a tank and that was brim tested and works out at 50+mpg. Although that run included 2 x 400 mile non-stop trips up to Glasgow at silly-o'clock. Am perhaps a more sedate driver than most as 2 days after getting the car was told had tickets to the opening ceremony of the Olympics, didn't know how to use the cruise or speed limiter and was stopped on the M4 and 6 points followed. So a case of RTFM
A word of advice, don't go for an early (05 or 06) if buying the oil burner as they are fitted with inferior injectors and it's £££ to change them.
I specifically went for an 07 as it a) Had updated injectors and b) Didn't have a DPF (these came in a year later). Non DPF will have 7GN on the sticker near the spare wheel 7GG will be a DPF fitted model.
Since owning I've had a battery (sub £100 to replace) and a faulty alternator (£35 to have original refurbished). Also you must buy VAGCOM/VCDS as it pays for itself in the first year of ownership...and you don't have to deal with £120 scans from dealers.
Only mods made are the remap, quad zausts, towbar and upgrading summer rubber to 245/45/18 Pilot Super Sports, which now means my speedo reads accurately.