"Unfortunately, our tests suggest that the remarkable results of Apple's published tests aren't reflected in most of the real-world applications we tested. Based on our initial tests, the new Core-Duo-based iMac seems to be 10-20 per cent percent faster than its predecessor when it comes to native applications, with some select tasks showing improvement above and beyond that,"
That's not entirely fair, as Mac software has not had much time to become optimized for the newer processor. As it stands right now, though, these Intel-using macs are failing to impress even some of the most die hard fans. As the software matures, we may see this change, and quite a bit – but don't count on it being a performance king.