In multimedia. Video encoding. I bet it will, but most free apps will take longer to be updated. Professional apps will take advantages asap. DivX is also ready for it.
If you are going more future proof the 9450 is a great idea. Its higher FSB does mean you need a better board when overclocking, but most boards do high FSB easy now.
Without overclocking it already beats the Q6600 due to its higher speed and some slight core enhancements.
The Q6600 is flocked to for its low price and good performance and overclocking for the price
The Q9450 also uses less power so its a more green solution.