Rambus also costs a ****load of $$$. It also doesn't perform any better than DDR, heck PC133 system configurations. We have a bunch of RAMBUS systems in the office, they cost like $6000 CDN and the tech support lead ran a bunch of benchmarks (no, not Q3a, not Sandra... real world applications tests, apps which our company uses) and his conclusion was that they ran not faster, but SLOWER than exisiting workstation configurations.
So, all the hype, specs fluff are just marketing $$$. Your system may run nice and fast but bring it in and we'll get a P3/PC133 combo that'll make you cry about all that cash you tossed out the window to some marketing hype.