PS3Fanboy have a nice summary of a recently published GameDaily article that outlines what you are getting with each of the different SKU’s. While the $500 SKU, without high definition support or Blu-Ray, seems to represent some value, they have worked out that with the $600 SKU you are effectively get around $1,200 worth.
$500 SKU
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"$600 PS3 is Effectively Half Price" - 11.07.06