Temp sensor went out at around 45K...took about 10 minutes and 10 dollars at the local parts store to replace.
The motor for the slide-back sunroof broke... replacement was too expensive at the time (broke college student) so I simply used the manual hand crank inside the control box on the ceiling.
Was totaled by the side impact of a dump-truck that ran a stop-sign. (however I can't really fault the car for that... although the fact that I'm still alive speaks wonders for the saftey factor of the car)
Great car... fantastically reliable. Started first time, every time... even when the temp dropped to -17 F.
It was driven hard by a broke college kid (me) and didn't receive all the maintenance it should have and still it kept running perfectly.
If they still made these I'd most certainly buy another one.
Volkswagen still does make the Quantum, they call it the Passat now. I doubt though that the new Passat is anything like the old Quantum.
I agree with the reliability... but forget about it when any Quantum gets over 100,000; nothing but problems.