I have the '06 VW jetta TDI with DSG. I am in love with the car, I love to drive it. It is truly a "sports car lovers" economy car. Only 42K on it right now, but it is doing great.
I did have one problem with the car early on, but to VW's credit, they paid for the rental car and made 1 car payment. I consider that issue (a bad solenoid in the trans valve body) to be fully made right by VW.
I get 42MPG fast highway, 35 city. Worst 34, best just a tick under 65MPG. I did that one by driving 1 lane highway back roads at 49MPH instead of 55. I coasted to a stop using 1/2 mile each time, AC, fan and headlights off. (yes I have to mod to turn off the lights).
I have never tried biodiesel in the car, as there were some 'net reports that VW would not cover fuel system related failures if Bio was detected in the tank.
I hear what the above poster says about Mexican VW's. Not likely to be a problem, as the engines and trans are not made or assembled in Mexico. The engine is Polish and the trans German.
Also, the Europeans require all car components to be recyclable. That results in very poor rubber quality along with short life hoses, plastic, seat foams, HVAC ducting and foams etc. This includes the paint! Mexico is not subject to such regulations. So the better paint and rubber and plastics come out of Mexico.
Ask any Mercedes or Audi mechanic what happens to the older ones. They deteriorate quite early. 5 years in Florida!
Chris