Intel has made a system that for the most part alleviates the need for more memory bandwidth. Three channels of DDR3 means we're saturated with it from the word go, and for the most part spending big money on faster performance memory has a unnoticeable effect.
For games, it does nothing in the real world because the bottleneck is firmly elsewhere: either the threading capability of the game, the clock frequency of your CPU (not the Uncore) or the graphics subsystem. For other things, we're still limited for stuff like IO and storage bandwidth - so while people complain about memory use, having programs use up a big chunk of 6GB (or more) benefits performance because we're not limited by measly hard drives.
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Original URL, circa 2009: http://www.bit-tech.net/hardware/cpus/2009/01/26/intel-core-i7-memory-performance-review/1