Just look at Button... He couldn't win a grand prix in over 200 races. Then he went to Brawn, and he became world champion (ok, he won one race before that, but just because everyone else dropped out). Brawn had the best car, so he won. In the latter stages of last year, the other teams caught on, and Button didn't win anymore. This tells me that it is the car that makes the biggest difference. Button is maybe a good driver (although I don't think so), but without a great car, he is useless.
When looking at Vettel, he did great with the Torro Rosso, bad car, but he made it look great. I am sure if you put any of the minor drivers (Beumi, Algesauri etc.) in the Red Bull they will not win a grand prix, but they will finish in the top 5, because they have a great car. One of the best drivers of all time, Michael Schumacher is struggling because he has a bad car (given he isn't at his best).
What I am trying to say is that, according to me, the car is about 60-70% and the driver fills the rest. I am sure if you put Vettel in the Hispania car, he will not be 3-5 seconds off the pace, but will match the Force India on pace, just because he adds that bit more. Put Senna in the Red Bull and I am sure Red Bull won't win a race. So yes, it is a combination of both, but I think the car place a bigger part than the driver.
Only my 2 cents worth.
