The 15" and 17" models now use the i5 and i7 Intel dual-core processors (at 2.4, 2.53GHz or 2.66Ghz, respectively -- gigahertz numbers no longer displayed quite so prominently on the product page), giving them a big performance boost and permitting hyperthreading (up to 4 virtual cores).

[tuaw.com...]

[apple.com...]